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 Valve Lifter, Guides, Retainers & Bolts
Courtesy of GENERAL MOTORS CORP.
Loosen the valve lifter guide hold down bracket bolts.