WARNING: This page is about a different car, the 2007 Chrysler PT Cruiser. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Locating Center High Mounted Stop Lamp & Cover
Courtesy of CHRYSLER LLC
Open liftgate.
Remove liftgate CHMSL cover.
Unsnap and remove the CHMSL lens from the lamp housing.