Shark is one of the brand names of Euro-Pro Operating LLC, and it includes several vacuum cleaner models. Some of these have a rotating brush to facilitate dirt pickup driven by a belt attached to a small engine in the cleaning head. Newer models include an emergency cutoff that stops the brush if it gets clogged, and the company claims that this feature protects the belt so well that it should last for the life of the appliance. If the belt does break, or you have an older Shark vacuum, replacing the belt is no problem.
Unplug the vacuum, remove and empty the dust cup, if applicable, and lock the vacuum in the upright position. Lay it flat on the floor so you can access the brush roller.
Remove the screws holding the roller cover, using a flat-head or Phillips screwdriver, depending on the model. The location of the screws depends on the vacuum model, but they are always easy to spot.
Grasp the end of the roller farthest from the belt and angle that end out of the holder. As soon as it's free, remove the other end of the roller. If the old belt is still attached, slip it off the roller, then off the motor shaft.
Clean the brush roll thoroughly, using a hairbrush, scissors and pliers -- if necessary -- to remove old hair and debris. Avoid cutting the bristles.
Slip a new belt around the motor shaft, then slip it around the roller and seat. Grasp the roller at both ends and pull it away from the motor shaft, keeping equal tension on both ends.
Insert the end farthest from the belt partially in the holder in the vacuum head, then pull the other end tight and seat it partially in its holder. When both ends are seated, push them all the way in.
Replace the brush roll cover and secure it with the screws you removed. Set the vacuum upright, plug it in and test the roller.