Replacing rear speakers in 2003 Impala?

[mkjt88]

I put down the seats, took out 4 bolts and a few plastic pop screws? Not sure what they are called but they push in tighter and are hard to pop out. Then once those are out I got the carpeted rear deck piece, that has the build it grills, out and the speakers and mounts are visible. I got under that in the trunk and pushed the two clamps in and trying to push them up and out now but they won't move.. They are not screwed in and was wondering if maybe the factory speaker mounts are glued in? If anyone can help me get these out it would be very appreciated, thanks.