How do you replace the serpentine belt on a 1999 Buick LeSabre?

There is a spring-loaded tensioner pulley that keeps tension on the belt. The tensioner should have a place to fit a ratchet wrench or breaker bar (may or may not need a socket). The tensioner bar rotates clockwise or counterclockwise to release the tension on the belt. Be sure and note how the belt is routed so you will install the new belt in the same pattern. The tensioner is self-adjusting.