Locate the drive belt tensioner. On most Murray mowers, it's a long bolt with a nut on each end, located near the center of the mower deck.
Loosen the lock nuts on the tensioner. Use a wrench to loosen the nuts enough that the tensioner can move.
Turn the tensioner bolt clockwise to tighten the drive belt. Tighten the bolt until the belt is snug, but not too tight.
Retighten the lock nuts on the tensioner. Use the wrench to tighten the nuts until they are snug.
Test the drive belt tension. Push down on the belt with your thumb. It should deflect about 1/2 inch. If it deflects more or less than that, adjust the tensioner bolt accordingly.
