i need instructions on how to change a belt on a bolen riding lawnmower?

Answer 1

Which belt is it? The drive belt for the transmission or the deck belt?
Well, pretty much either way the deck will need to be removed to gain acess to both. the deck will have guards that need to be removed to put the belt on the pulleys - if the old one is still on- make a drawing of how it looks before removing it.
To remove the deck :
Depends on the brand tractor, but normally a few pins hold it on the tractor - again make notes of where they all go before removal. The deck belt is held on the crank pulley by two or three retaining bolts ( helps keep the belt from comming off), these need to be unscrewed to get the belt off.
I usually raise the front of the tractor with a jack under the front axle to slide the deck out easliy, just make sure the rear wheels are chocked to prevent rolling.
The drive belt underneath will be a bit trickier , sometimes theres guide plates in the way that need removing. Again make a drawing of the configuration before removal. There will be belt retaining pins on the trans drive pulley. After all the pins and retainers are removed , push on the clutch, itll release tension on the belt , so itll come off. There might be two drive belts - both attached to a center pulley . Your local autoparts store carry replacement belts - just mention heavier duty for a lawntractor, plus if you still have the belt, they can match up the numbers.
If you have any questions let me know

Answer 2

Most of the newer mowers have a diagram on the deck for deck belt replacement and a diagram for the ground motion belt somewhere on the tractor. Look under the hood or under the foot rests.