1996 toyota tersel Squealing fan belts. Tighten or replace?

I'm not familiar with that particular vehicle but generally in the older cars with v-belts driving the alternator, fan and water pump, the belt will begin slipping with wear and must be adjusted tighter. Usually means loosening an adjustment (like an alternator bolt or two) and tightening the belt.

If the belt has been slipping for a long period of time, it's probably glazed and burned, requiring replacement. Look online for a manual (youtube?) for a procedure, or find a maintenance manual for your car.