WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Loosening Side Window Air Outlet Grille (Rendezvous)
Courtesy of GENERAL MOTORS CORP.
Use a small flat-bladed tool to release the side window air outlet grille.
Fig 2: Identifying Side Window Air Outlet Grille (Rendezvous)