There are special tools that are used to remove and install the torsion bars. The procedure is out lined below. You may be able to use large screwdrivers or fabricate a tool to do this work.
Rear Compartment Lid Hinge Torque Rod Replacement Removal Procedure
Important: Properly seat the torque rod between the rear shelf and the hinge assembly.
Tighten Tighten the bolts to 18 N·m (13 lb ft).
Not able to view the GM links Is that normal?
If you'd like to see what one of the tools looks like, check the link below. Don't have a better picture of the other lever tool.