If it is a Magnum, you don't need tools, just strong hands. Carefully squeeze the two halves of the rear pully apart to have the belt creep to the middle of the pulley. Then you just slip it off the front pulley and work it off the back. Reinstallation is the reverse. Set the belt on the rear pulley and squeeze them apart ot have the belt drop in, then loop it around the front. Next time you pedal it, the belt will adjust itself automatically. Just be aware that you can pinch your fingers if you are not careful.
On a TFR, you have to loosen the muffler and engine mounts and slide the motor back to remove the belt, then readjust it by sliding the motor forward after installation. Don't forget to tighten the muffler.
Any auto parts store should be able to match up the belt.
A note on belts: they seldom break. You can loose a chunk of rubber from the part that rides in the groove and still use it to get home. If the outside of the belt has a tear, it will surely go. The strength of a belt is on the outside. The rubber portion that rides in the pulley just gives it grip. My Vespa Grande is missing a small chunk of rubber and it's still holding up after more than 500 miles.