Lastly the alternator, loosen but do not remove the adjuster bolt at the top that is in the groove that allows you to slide the alternator back and forth. Then loosen the pivot bolt on the bottom of the alternator, it is sort of under the pulley and slide the alternator toward the front of the vehicle relieving the tension on the belt. Now unlike the other two belts that have adjustment screws, the alternator has a tab for a pry bar to set the tension. With the new alternator belt on pry the alternator toward the rear of the vehicle, while holding it there with a pry bar, tighten the adjuster bolt. It can be done by yourself, but is easier with a buddy.
From the link above.
