Consult the treadmill manual.

• 1). Before attempting to repair your treadmill, read the manual. Manuals often contain detailed information on how to perform routine maintenance to keep your treadmill running smoothly.
  
  Generally, maintenance techniques will be listed separately toward the rear of the manual or in the troubleshooting section.
  
  If you have misplaced the manual, try finding it online. Many treadmill manufacturers provide free access to manuals or offer a customer service phone number. Service representatives can often answer basic maintenance inquiries at no charge.
  
  
• 2). Locate the screws for belt adjustment. Most treadmill belts can be adjusted using the belt screws. Often they are located toward the back of the treadmill near the roller axle. The adjustment screws usually have a six-sided head called a hex.
  
  Hex screws must be turned using a hex key or Allen wrench. Normally, the wrenches are supplied at delivery by the manufacturer. If you do not have an Allen wrench, you can pick one up relatively cheaply at most home-improvement stores.
  
  
• 3). Turn on the treadmill. When adjusting the belt, you should run the treadmill at a low pace around three miles per hour or less.
  
  
• 4). Turn the belt adjustment screws. If you need to tighten the walking belt, begin turning the hex screws one-quarter turn clockwise. Turn each screw the same number of times so that both are equally tightened.
  
  If the belt is too tight, loosen the screws by turning them one-quarter counterclockwise. Again, turn each screw equally.
  
  If the belt is not centered properly, turn the left screw to move the belt toward the left side. Conversely, turn the right screw to move the belt toward the right. A properly centered belt is essential to avoid premature fraying.