How do you de-tension the serpentine belt on a 1995 Chevy Cavalier?
If your car has a tensioner pulley it can be moved to release the tension on the belt for removal. Make note of the routing of the belt before removing it. This will make installing the replacement belt much easier. If you do not have a tensioner pulley one of your accessory motor/pumps (most likely your alternator) can be moved in order to release the tension on the belt.
Most tensioner pulleys have an hole the exact size of a ratchet drive on the tensioner arm. This allows you to put a standard ratchet (without any socket attached to it) into that hole and use the leverage of the ratchet to release the tension.