Remove the key from the ignition and disconnect the spark plug before servicing your riding mower. Wear thick work gloves to protect your hands from sharp components.
Take out the bolts or screws securing the drive chain cover; the type and number of fasteners varies by riding mower brand and model. Set the removed cover and hardware aside.
Open the master chain link with a small flat-head screwdriver. Break the chain, using a chain tool, if it doesn't have a master link. Align the chain tool probe with one of the link pins in the riding mower chain. Turn the chain tool handle to force out the desired link pin and break the chain.
Slip the chain off the drive system. Straighten the removed riding mower chain and place it on a padded surface.
Use the chain tool to remove an unwanted link. Line up the tool probe with the pin in the last chain link; turn the handle to force out the pin and free the link. Repeat this step to remove additional links as needed.
Fit the two end chain links together and reinsert one of the removed pins. Hold the chain tool against the pin and turn the handle to push the pin into place.