You need to pull off the trim piece around the radio (black rectangle).
Use the Kenwood key to pull out the head unit.
If you don't have the key, you can release the pocket and the head unit from the back by removing the glove box and pushing the clips on the back side.
As for the rest, if you're planning to run a much stronger amp, you'll need bigger power and ground wire as the stock stuff is only 10 or 12 gauge.
Good luck!