WARNING: This page is about a different car, the 2006 Dodge Magnum, 2006 Dodge Charger, and 2006 Chrysler 300. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Removing/Installing Rear Wiper Arm
Courtesy of DAIMLERCHRYSLER CORP.
Remove the nut cap (2).
Remove the retaining nut (1).
Gently rock the wiper arm from side to side to loosen it from the shaft.