Replacing an alternator

how do i replace an alternator and where exactly is it i have a '99 olds eight eight

Wow ,you don't know where it is under the hood, not a good start here! Check the info at autozone.com, repair guides.

This model has the Series II 3800 engine. The alternator is located on the right top side of the engine. Right meaning passenger side.

All you have to do is remove the serpentine drive belt via the tensioner assembly. The tensioner has a 15mm bolt that you turn counter-clockwise to loosen the drive belt. But first be sure to disconnect the battery negative cable. And then undo the electrical connectors and red output lead to the battery. There should be at least three bolts that hold the alternator down on to the mounting bracket.