I am sending you instructions right out of the GM service manual for your car. Be sure the radio is turned off before unhooking the battery as we don't want it going into the theft lock up mode. See below. Thanks, Bob
Important: Do NOT tip the battery more than 40 degrees during removal.
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Tighten Tighten the bolt to 18 N·m (13 lb ft).
Tighten Tighten the terminal bolt to 15N·m (11 lb ft).