How to delete Key Fob's?

Your car allows a maximum of 4 key fobs to be programmed into it. From your description I would say that someone had already added at least 2 onto the factory 2. There are 3 ways to program in new fobs on that car. The first one is likely the one you are using that shows that all of the spaces are taken. The next method uses a scan tool to go in, erase all of the fobs and then you can add the three you have back in. This is actually the easiest and safest way to do the process.
The third method is below It takes the longest time of all methods and if you make a mistake you have to start over from the beginning. Pay very close attention to the warnings as you can also cause the fobs to be useless if you miss the last couple of steps.

Method 3 - Erasing/Adding Key Fobs (No Known Fob Available)

This procedure will first erase all known key fobs. The procedure will then program a single key fob or multiple key fobs. Method 3 is a series of three 10-minute key cycles, for a total of 30 minutes. This procedure requires that you have a replacement key fob and the vehicle's mechanical key.

Important - Do not place any known good key fobs within 10 feet of the vehicle when programming with Method 3. If the RCDLR recognizes a known good key fob during Method 3 programming, the programming mode will resort to Method 1.

1. The vehicle must be OFF.
2. Place the new/replacement key fob in the console pocket with the buttons facing forward.
3. Insert the vehicle key in the driver door lock cylinder located in the driver door handle and cycle the key 5 times within 5 seconds.
4. The DIC will display a message: OFF/ACC TO LEARN.

5. Press the OFF/ACC portion of the ignition button.
6. The DIC will display a message: WAIT 10 MINUTES, and then begin to count down from 10 to 0, one minute at a time.
7. When the counter reaches 0, DIC will display OFF/ACC TO LEARN.

8. Repeat steps 5-7 two more times, for a total of 30 minutes.

9. At the end of the 30 minute cycle, a beep will occur and the DIC will display: READY FOR FOB 1. At this time all previously known key fobs have been erased. When fob 1 is programmed a beep will be heard and the DIC will display a message: READY FOR FOB 2.
10. Additional key fobs can be programmed by taking fob 1 out of the pocket and inserting fob 2. If desired, up to 4 fobs can be programmed. Once 4 fobs have been learned, the DIC will display a message: MAX FOBS LEARNED, and automatically exit the program mode.
11. If learning less than 4 key fobs, press the OFF/ACC portion of the ignition button to exit the program mode.

Important - Failure to exit programming mode (press OFF/ACC) prior to pressing the UNLOCK button of each key fob programmed will result in that fob being inoperative. Pressing the UNLOCK button completes the programming sequence and is require to ensure transmitter operation.

12. Press the UNLOCK button on each key fob that was programmed to finalize the programming and confirm system operation.

You would be better off using a scan tool to go into the system to do what you want to do.
But these are the other methods

Method 1 is also used for the initial programming of fobs to a new replacement RCDLR. In this instance, the new RCDLR comes ready to learn the first key fobs introduced. Perform the learn procedure as outlined, with the exception that the new RCDLR does not require a known good key fob to be placed within the interior of the vehicle.

Important: This procedure is not available when the maximum number of fobs (4) have been programmed. If 4 key fobs are programmed to this RCDLR and this method is attempted, the driver information center (DIC) will display MAX FOBS LEARNED and the programming procedure will exit. Methods 2 or 3 must be used in this instance.

1. The vehicle must be OFF.
2. Place a known key fob and any new/replacement key fob(s) to be programmed in the cupholder inside the vehicle. DO NOT place any fobs in the console fob pocket at this time.
3. Insert the vehicle key in the driver door lock cylinder located in the driver door handle and cycle the key 5 times within 5 seconds.
4. The DIC will display a message: READY FOR FOB X (X = fob 2, 3, or 4).

If the DIC displays: OFF/ACC TO LEARN, the known fob has not been recognized. At this time, programming will revert to Method 2.

5. If the DIC is displaying the correct fob number that needs to be programmed, skip ahead to step 9.
6. If the DIC is not displaying the correct fob number that needs to be changed (i.E, the DIC is displaying: READY FOR FOB 3, and you wish to program FOB 1), use the scan tool to access the following
* Vehicle Control Systems
* Computer/Integrating Systems
* Module Setup
* Remote Control Door Lock Receiver
* Program Key Fobs
7. Select the fob position you wish to program:
Important Selecting Invalidate All Fobs will erase any known fobs and will cause the DIC to prompt READY FOR FOB 1, requiring all fobs to be relearned to the vehicle.

* Invalidate All Fobs
* Program Fob 1
* Program Fob 2
* Program Fob 3
* Program Fob 4

8. With the fob position selected, press the PROGRAM soft key on the scan tool. The DIC should display: READY FOR FOB X (X = fob 1, 2, 3 or 4, depending on the selected position)
9. With the DIC displaying the correct fob position that is to be programmed, place the new/replacement key fob in the console fob pocket with the buttons facing forward.
10. A beep will occur once the fob has been learned.
11. If programming additional key fobs and there is no DIC prompt that indicates READY FOR FOB X, repeat steps 7 and 8.
12. Exit programming mode by pushing the OFF/ACC portion of the ignition switch.

Important: Failure to exit programming mode (press OFF/ACC) prior to pressing the UNLOCK button of each key fob programmed will result in that fob being inoperative. Pressing the UNLOCK button completes the programming sequence and is require to ensure transmitter operation.

13. Press the UNLOCK button on each key fob that was programmed to finalize the programming and confirm system operation.

Method 2 - Erasing/Adding Key Fobs (No Known Fob Available)

This procedure will first erase all known key fobs. The procedure will then program a single key fob or multiple key fobs. Method 3 is a series of three 10-minute key cycles, for a total of 30 minutes. This procedure requires that you have a replacement key fob and the vehicle's mechanical key.

Important: Do not place any known good key fobs within 10 feet of the vehicle when programming with Method 2. If the RCDLR recognizes a known good key fob during Method 2 programming, the programming mode will resort to Method 1.

1. The vehicle must be OFF.
2. Place the new/replacement key fob in the console pocket with the buttons facing forward.
3. Insert the vehicle key in the driver door lock cylinder located in the driver door handle and cycle the key 5 times within 5 seconds.
4. The DIC will display a message: OFF/ACC TO LEARN.
5. Press the OFF/ACC portion of the ignition button.
6. The DIC will display a message: WAIT 10 MINUTES, and then begin to count down from 10 to 0, one minute at a time.
7. When the counter reaches 0, DIC will display OFF/ACC TO LEARN.
8. Repeat steps 5-7 two more times, for a total of 30 minutes.
9. At the end of the 30 minute cycle, a beep will occur and the DIC will display: READY FOR FOB 1. At this time all previously known key fobs have been erased. When fob 1 is programmed a beep will be heard and the DIC will display a message: READY FOR FOB 2.
10. Additional key fobs can be programmed by taking fob 1 out of the pocket and inserting fob 2. If desired, up to 4 fobs can be programmed. Once 4 fobs have been learned, the DIC will display a message: MAX FOBS LEARNED, and automatically exit the program mode.
11. If learning less than 4 key fobs, press the OFF/ACC portion of the ignition button to exit the program mode.

Important Failure to exit programming mode (press OFF/ACC) prior to pressing the UNLOCK button of each key fob programmed will result in that fob being inoperative. Pressing the UNLOCK button completes the programming sequence and is require to ensure transmitter operation.

12. Press the UNLOCK button on each key fob that was programmed to finalize the programming and confirm system operation.