I am trying to replace the front brakes but I can't get the caliper to retract

Hello,
The piston in the caliper can be retract using a caliper tool that presses the piston or a large C-clamp.
Before trying to retract the piston, be sure to remove the brake fluid reservoir cap.

Here is a helpful guide:

https://www.2carpros.com/articles/how-to-replace-front-brake-pads-and-rotors-fwd

If you are still unable to push the piston back in that it is probably seized and the caliper needs to be replaced.

https://www.2carpros.com/articles/brake-caliper-replacement

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.