How do you get access to underneath and behind the rear seat of a 2003 Mustang Convertible Pony to fit seat covers?

There are two small buttons underneath the front edge of the seat bottom. You may need to pull the carpet back a bit to see them. You will probably be better off trying to feel for them. Press the button firmly. It will take some force. You will hear a pop and the seat will move slightly. You can do one side at a time.