Are you talking about the ceiling panel, and the associated "rails" on either side of it, in which you can not see any rivets? You might need to take that down first, in order to access the top of the wall panels. If that's what you're talking about, you can remove the ceiling panel by drilling out all the rivets you can see, and removing all the light fixtures, etc, that are attached through it. then, with some help, you can probably get the panel to bow enough without creasing it to get it to pop out of those long channels. With the ceiling panel removed, you'll see how the chanel is riveted on to the ribs; there's an "extension" that is hidden by the ceiling panel that is riveted to the ribs; once the panel is out, you can drill out those rivets, and take the channels down out of the way.
Or, you could do like I did, and just use a putty knife tucked up between the chanel and the ceiling, and tap it with a hammer to break off the rivets. after I got it apart, I realized that this probably wasn't necessary.
Oh, well. live and learn....didn't break anything. it was just alot more work than it needed to be....
while you're in there, take a good hard look at any aerial antennas that may be installed. they tend to leak like a sieve.
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