Around the trim piece there should be 6 clips, three on each side. With a panel removal tool (or a screwdriver with electrical tape on it to keep from scratching) it should pop right off. Then you should have 6 visible 9/32 screws. The top two on each side are for the stereo the the bottom ones are for the AC panel.
For 08's they used GM's 29-bit LAN bus so adapters MAY be needed in order for the car to continue to function correctly. (Some will just throw weird warnings others will be fine)
Pac part numbers:
C2R-GM29 radio replacement for cars without on star
OS-3 radio replacement for cars without Bose
OS-3BOSE radio replacement for cars with Bose
OS-4 radio replacement for cars with or without Bose and with On Star.