First off buy both belts. Everything needs to come apart so it's better to do both at the same time. Next take all the plastics off that you can. Next take a marker or pencil and mark the frame where the rear pulley axle is on both sides. Next mark both the bearings on the front axle on the frame. Now you know the exact position to put it back together. Next take the 4 nuts off the front bearings. Then the 2 off the rear tension pulley. Now everything is loose. Slide your belts over the pedal at the front and past the bearings and leave them off the pulley loose. Next slide the rear pulley back in. Next put all nuts and bolts on loosely. Next tighten front bearing bolts in position. Then put belts on the pulleys and adjust the rear.
Do you need more assistance? If not please rate my answer, thanks!