WARNING: This page is about a different car, the 2004 Subaru Outback, 2004 Subaru Legacy, and 2004 Subaru Baja. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect ground cable from battery.
Open tail gate.
Remove bolt cover.
Fig 1: Removing Bolt Cover
Courtesy of SUBARU OF AMERICA, INC.
Remove bolt and detach rear combination light assembly by pulling to the rear.