How do I replace an alternator belt on Toyota 2003 Highlander?

A lot of time the belt tightener will seize up and not move . if this happens take it off the truck and put it in a vice spray the living daylights out of it with your favorite lubricant (WD 40) or whatever and work on getting it to move once its moving freely return it to the truck and replace your belt. You can usually slide the belt from the idler to loosen the belt. Its always a good idea to snap a photo of the belt route before removing the belt so you know how to reinstall it