WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 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.