These instructions will help you . and also the picture below will help you more.
the belt-routing diagram, printed on the fan shroud or possibly applied
to the underside of the hood. This diagram shows you how to properly
route the new belt, as well as identifying the location of the various
pulleys, including the serpentine belt tensioner.
the belt tensioner off the Sable's belt using the serpentine belt tool.
The tool connects to the side of the tensioner's arm and essentially
acts as a handle for use in moving the tensioner. You can purchase a
serpentine belt tool at most auto-part retailers.
the belt away from the tensioner with your free hand and release the
pressure on the tensioner with the tool. Pull the belt off the rest of
the pulleys by hand and then remove it from the engine well.
the old belt and new belt with one hand and put your foot through the
other end of the belts. Stretch them both to their full length and check
to ensure their both the same size. The old belt may have up to
one-inch of extra length due to normal stretching that occurs during the
belt's service life.
the new belt, rib side to the pulley, around the crankshaft pulley.
Consult the routing diagram and route the belt to the next pulley on the
diagram. Continue to route and then check the diagram until you have
the belt wound around every pulley except the belt tensioner pulley.
check to make sure the belt routes exactly as shown on the diagram and
then move the tensioner aside once more so you can route the belt over
the tensioner pulley as shown in the diagram. Move the tensioner back
into place slowly and remove the tool.