I need to know how to change the drive belt 1998 Yard Machine tractor
Model # 13AM675G062.

Thanks,
Jim

Hi,
You have half the numbers needed to get a free copy of the manual. Just jot down the serial number also and go to:
PDF Manual Web Archive
Put them into the appropriate boxes and get it. It has the directions in it. You basically start by removing the panel between the seat and dash to gain access and begin with the back belt.
Peace,
Clarke

You can also call any sears store (since they sold the MTD yardmachines riding mowers) and give them the model number (under the back seat ) which you already stated above, and get the part numbers for the 3 belts needed (if you are going to change 1 why not all 3, sears parts are high cost but if you go to Amazon web site, you can get them for about 10% of what sears wants, IE 34.95 + $11 shippinghandling, or pay "damlow" prices website $4.69 + shippinghandling.
2. After gaining acces to belt area under shift lever by removing the plate (remove the screws holding the plate on), (make sure mower is off and battery disconnected as a starter solenoid is located in that area and could short and cause the starter motor to turn the big motor and cut your pinky off), use a short flat screwdriver to lever the belt out/off of the pulley's, (draw diagram of which belt goes to which pulley first), then install new belts, (the pulleys, have pins or short metal flanges to help keep the belt on , so you have to lever/pull the belt out between the pully and the flange or pin, and push/or lever the new belt back in, (be careful not to damage the new belt with the screwdriver). Make sure the new belts fit snugly and are all down in between the flanges/pin and on the pulleys. You may be wise to jack up the front of the mower to gain easier access to the front drive pulley and the front mower deck pulley,
For the mower deck belt, you will have to remove dust and debris protective "cap" (metal irregular shaped pulley cover) to gain acces to mower deck pulleys.
Best of Luck!