-Tighten the tensioner pulley bolt to loosen the belt.
-Loosen the bolt to remove pulley--then install new tensioner pulley.
-Loosen idler pulley bolt--install new one.
-clean all the pulleys w/ wire brush or scotch brite pad.
I just did this today--didn't help the squeaking at all.
Make sure you check all your pulleys for dirty/squeaking bearings; water pump, a/c, tensioner, idler, power steering, alternator. check for any play in the pulleys.
When the engines running look at all the pulleys for excessive wobble. crankshaft should wobble a little. Check you power steering fluid, I heard if it's low the belt (or maybe the pump) will squeak.
If all else fails and it's still squeaking, get a new tensioner--RockAuto has 'em for $40 + shipping.