The instructions say remove drive belt, remove the bolt going through the tensioner, (toward the top half of the tensioner), on installation of new tensioner insure the pin on the tensioner properly seats in the alternator bracket/housing. Part is $50 to $60 labor .7 to .9 hours approx.
First use a 3/8" inch ratchet or breaker bar to loosen the tension on the serpentine belt there is a little 3/8" square hole in the front of the tensioner where the bar fits. Then remove one bolt and replace the tensioner. If you remove the belt make a drawing of where it goes back before removal.