The drive belt or serpentine belt on a Ford Focus has no time or mileage criteria for replacement. The most effective way to ascertain the functionality of the belt is to inspect it for cracks in the grooved area and to look for fraying on the sides. If either exists, fitting a new belt is recommended. If the belt stretches past the tensioner, you should also replace the belt. The belt has stretched beyond its life if you can turn it more than 90 degrees when it is still on the pulleys.
Release the tension on the Ford Focus belt by inserting the ratchet into the tensioner. There is a square hole in the part of the tensioner opposite the pulley in an extended portion of the pulley. Insert the ratchet in the hole and push the ratchet toward the firewall to loosen the tension.
Remove the belt, observing the routing of the belt prior to removal.
Install the new belt, working counterclockwise, starting at the alternator. Wrap the belt around the alternator pulley, down to the inside of the tensioner, around the crankshaft, straight over to the air-conditioning compressor and up on the inside of the idler pulley. Slide the belt off at the alternator just enough to give slack so the remainder of the belt can be installed around the power steering.
Insert the ratchet in the tensioner and push the tensioner toward the firewall, which will give you enough slack in the belt so that it can be slid onto the alternator pulley. Release the tension on the ratchet and remove it.