Each belt on '97 sentra has its' own adjuster.
on the small belt loosen the locknut on the adjuster at the ps pump pulley
wheel.do this from under the hood. from under the car loosen the pivot nut
at the bottom of the ps pump. from the hood loosen the adjuster bolt until
you can free the belt with your hand. you will need a 12mm wrench for the
adjuster and its' locknut and a 14mm for the pivot bolt.

on the large belt just loosen, but do not remove the nut in the center of
the idler pulley wheel with a 14mm wrench. Then loosen the adjuster at the
forward pulley wheel with an 8mm socket using an offset adapter to get at
it until you can work the belt off by hand. All this must be done from
under the car.