WARNING: This page is about a different car, the 2008 Isuzu i-370, 2008 Isuzu i-290, 2008 GMC Canyon, and 2008 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: View Of Antenna Mast Removal Tool
Courtesy of GENERAL MOTORS CORP.
Use the tool (1) provided with the vehicle to unscrew the antenna mast.