goflow, if it is the mower drive belt you are replacing, follow the following instructions from the manual:
"TO REPLACE MOWER BLADE DRIVE BELT
The mower blade drive belt may be replaced without tools. Park the tractor on level surface. Engage parking brake.
BELT REMOVAL -
1. Remove mower from tractor (See 'q'O REMOVE MOWER" in this section of manual).
2. Work belt off both mandrel pulleys and idler pulleys.
3. Pull belt away from mower.
BELT INSTALLATION -
1. Work belt around both mandrel pulleys and idler pulleys
2. Make sure belt is in all pulley grooves and inside all belt guides.
3. Install mower (See 'q'o Install Mower" in this section of this manual).
You can get the manual from here. Hope this helps, good luck.