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: View Of Liftgate Door Sill Plate
Courtesy of GENERAL MOTORS CORP.
Open the lift gate.
Pull up to remove the door sill plate from the vehicle.