Actually, on the sedan it is a little more involved.
In order to remove the center brake light, you have to remove the rear deck as the deck is moulded around the brake light.
In order to do that you have to remove your rear seat. First remove the seat bottom. It is held in by one clip on each side. There should be a tab you can pull which releases the clips. Then you remove the seat back. It is held in by 6 bolts (I believe); 4 at the bottom, and two behind the headrests. Completely remove it by lifting up and out. There are two hooks at the back of the seat that slide into holes behind the seat.
Once you have that out, you have to remove the side post moldings. Each is held on by a single screw and several clips on the edge.
NOW you can remove the panel. It is held down by, I believe, 4 clips on the front edge. Carefully pry up at the clips so as not to damage the panel. Once you have those released, you can slide the rear deck panel out of the way.
As mentioned above, the center brake light is secured by two nuts which can be accessed through the trunk. Loosen these and slide the light back, and out.
PS. Sorry, I missed out one step, and that is the part where you have to remove/disconnect your speakers before you can take the panel off.