WARNING: This page is about a different car, the 2007 Pontiac Montana SV6, 2007 Chevrolet Uplander, and 2007 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
Loosen the screw at the rearview mirror support.
Fig 1: View Of Rearview Mirror
Courtesy of GENERAL MOTORS CORP.
Slide the rearview mirror from the rearview mirror support.