How can I loosen up tight vacuum cleaner belts?

Answer 1

if you have the right one you don't want to ,period,something is wrong

Answer 2

Very few vacuums have adjustments for tension of the brush roll drive belt. Those that do use small screws in the frame of the motor to be loosened so the motor can be moved back or forward to tighten or loosen the belt. Fully 98% of the vacuums on the market today use either a flat or round rubber band, in effect, to drive the brush roll. It has to be quite tight or the brush would stop as soon as it hits the carpet. You're probably wasting your time to try to loosen it.