Here are directions
With the dashboard facia pulled off you should now see 3 screws holding the factory radio in place. Undo those and gently remove the radio. There are three cords entering the back of the radio, the grey one is the antenna, pull it straight out. The other two are the factory harness, they are VERY tough to get out. Push down on the tab to release the harness plug and pull straight back. You may need a flathead screwdriver to help push the harness plug out of the back of the radio.
The radios have the vehicle's VIN number programmed into, so you will have to have that programmed into it. That can only be done with a GM scanner. Should cost 1/2 hour labor for dealership to do this.
The radio looks for the vin number on the cars comm line and compares it to the stored one. If it does not match, it locks up.
To setup a new radio for the vehicle, complete the setup procedure under the Special Functions menu of the scan tool. Cycle the ignition. Setup is complete.
Important: The Radio Setup option does not contain a submenu. Radio Setup will configure the following systems: