You have to pull your back seat and your package shelf from inside the car to remove it, trust me I know. I installed a GTP overlay over my 3rd brake light...
Its been awhile but...
Back seat is held on with some tabs on the bottom section, pull out tabs and move up seat on both sides, back seat bottom can be removed. For the seat top, remove a couple bolts and its hooked in. Seat should pull up and out with the seat belts. From there you should see how to take out the seat belts pass through from there it SHOULD pull out. The brake light should slide out too.
Its been 5 years amd thats to the best of my memory....