There is an automatic tensioner that keeps tension on the belt. THere should be a label in the engine compartment somewhere giving you a diagram of the path of the belt and showing where the tensioner is and which way it turns to loosen the tension. On the 1995 GMC Sierra that I just worked on, I loosened the nut on the front of the tensioner a little, then I used a big pipe wrench on the tensioner itself to rotate the tensioner assembly counterclockwise then removed the belt while still holding the tensioner, then gradually released the tensioner. From looking at it I guess there is a special tool you can use to do this, you might want to check with Advance Auto. or whoever your closest auto parts store is to see if they will loan you the tool.
If it is a serpentine belt, the tension is automatically adjusted by the tension idler. If the belt is loose then the tensioner needs replacing. If it is a normal drive belt, then the alternator is mounted on a slotted bracket that allows you to adjust the position of the alternator. You can loosen the bolts and adjust the tension on the belt.
Loosen the alternator tensioner bolt. You will be able to slide the alternator either way to adjust the tension on the belt.
If it is a drive belt and not a serpentine belt is has no tensioner. You manually adjust the tension by normally adjusting tension by moving the alternator. Loosen to bolts holding the alternator in place and then adjust the tension. Tighten the bolts when the tension is right. If it is serpentine belt if you follow the belt around the the engine you will see the tensioner.
if the car doesn't have an automatic tensioner than if the belt is around the alternator pully you loosen the bolt holding the alternator on and move the alternator to tighten the belt.
loosen the alternator
You must first loosen the alternator, do not remove it. remove the alternator tension screws top and loosen the bottom screws DO NOT REMOVE push the alternator toward engine, for the a/c belt you must loosen the belt tension pulley and move it. replace in reverse order
autozone.com has online manuals that give step by step how to You tighten the tensioner on the bracket holding the air conditioner to loosen that belt then you turn the hold that adjusts the tension on the alternator shifting it forward to loosen that belt. You will have to take the AC belt off first, then the alternator belt.
First you will need to loosen the tension on the belt in order to remove the belt. After that, you will need to remove the bolt holding on the alternator. Installation is the reverse. Dont forget to tension the belt
loosen the bolt in the center of the drive belt pulley, then loosen the bolt on the side of the pulley. as you loosen the side bolt the tension lets up
loosen the tension on the belt with the tension pulley, remove the belt then disconnect your wires from the alternator then take the 3-4 bolts, holding the alternator on, off. then do the opposite to put the new one back on
Disconnect the positive battery cable, loosen the tension on the drive belt for the alternator, remove the electrical connections to the alt, remove the alt, and reverse the procedure. Tighten the drive belt tensioner to the required factory specs. Reconnect the battery cable.
Loosen tension regulating bolt for the alternator and the bolt attaching it the engines body, shift the alternator down and remove the belt. Install new one. Use regulating bolt to set proper tension. If you do not have tension meter, tighten until you can twist the belt only 3/4 of full turn.