Lay the chainsaw on its side with the blade side up.
Remove the safety cover that protects the operator's hands from the chain with a screwdriver.
Locate the oil pump adjustment screw located on the cap over the chain sprocket. The adjustment screw typically comes set in position "2" from the factory. This is suitable for a bar length of 15 to 18 inches.
Rotate the adjustment screw clockwise for a shorter bar and counterclockwise for a longer bar.
Reinstall the safety cover reversing the process used to remove it.