Unplug the saw from the power source.
Consult the saw's instruction manual for the specific length of belt tailored to the saw's motor. If the manual is not available, take the belt, either whole or broken, to where replacement belts are sold to determine the approximate length. A stretched belt is longer than the original belt, so a slightly shorter belt is the correct length.
Loosen the motor from the guide rails using a wrench or screwdriver. The motor must be loose enough to allow the belt to slip off the drive wheels. Loosen the motor even if the belt has broken. You will be readjusting the motor after you replace the belt.
Slip the new belt onto the motor drive wheel and then onto the saw blade drive wheel. The drive wheels of the motor and saw blade have a slight V configuration, as does the belt. The wheels and the belt should engage.
Pull the motor away from the saw blade until the belt is taut, but not so much that the saw blade cannot be turned easily by hand.
Tighten the bolts or screws that hold the motor to the guide rails.
Insert a wooden dowel rod or a screwdriver to engage the blade's teeth against the table saw body to prevent the large nut holding the blade in place from turning. Loosen the nut.
Remove the blade, paying attention to the orientation of its teeth. Attach the replacement blade in the same orientation. Tighten the holding nut onto the blade's axle.