WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Compartment Sill Plate Replacement - Rear
Courtesy of GENERAL MOTORS CORP.
Callout
Component Name
1
Rear Compartment Sill Plate Assembly Tip:
Release clips from the top of the sill plate first.