I need to replace the alternator

First make sure you note how the belt is run so that you can replace it in the same manner. there may be a routing diagram somewhere either on the underside of the hood or on/near the radiator shrouding. make your own if not. next find the tensioner pulley--black, kind of round, with smooth running surface. stick the proper sized wrench into the center of the tensioner pulley and twist. this should allow you to loosen the belt enough to remove it from any one of the other pulleys. These guides can help us fix it.

https://www.2carpros.com/articles/how-to-replace-an-alternator

and

https://www.2carpros.com/articles/replace-serpentine-belt

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.