How do you change a serpentine belt on a 1997 Chevy Tahoe 4WD V8 w ac alternator voltage type unknown?

Near the top of the engine is a tensioner assembly. The pully can be pushed back using a breaker-bar and the appropriate sized socket. Note the layout of the belt before removing it because there won't be much help if you can't figure out how to put it back. For the record, all GM vehicles since mid 50's have been 12 volt.

--improved response--

The belt tensioner pivots with spring tension against the back (smooth) side of the belt. The tensioner arn has a molded square hole in it - this hole takes the end of a 3/8" drive socket wrench, which you then use as a handle to give you leverage to go against the tensioner spring with one hand, while removing the belt with your other.