Replacing shift knob inside the car

That knob is molded to the top of the lever. Under it the shift lever looks like a T. As such replacing just the knob is not possible. You need to replace the knob and the lever that extends down into the console and to the shift control. This is not as hard as it sounds as the bottom of the lever is threaded as seen in the picture. The picture is not showing the rubber boot or the jamb nut that is between the lower linkage and the bottom of the shift housing though.
To remove it you need to remove the wood trim panel. To do that you first remove the interior ashtray insert. Now look inside the tray housing and you will see two screws. Remove them. Now pull the tray straight out of the dash. Now remove the coin tray by tipping the front of it up and rotating it back to release it. Now for the shift cover. Gently push it forward and up to release the clips that hold it in place. Disconnect the window switches and set it aside. (If the wood is loose or damaged, this is a good time to repair/replace it.) Now that the cover is off you need to remove the shift light from the side of the housing. Next look down into the console and you will see the three 10mm bolts that hold the cover in place. Remove them and lift up and turn the cover sideways to get to the jam nut. Release the jam nut and unscrew the shift nob/lever from the lower unit.

Reverse the process to install the new knob/lever. If you want a different knob than stock there are some available or you can build a lever to replace the old one and thread the top to fit whatever you wish.