WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: View Of Floor Air Outlet Duct
Courtesy of GENERAL MOTORS CORP.
Remove the push pin (5) from the left floor air outlet duct (4).
Remove the left floor duct (1) from the HVAC module (2).