Craftsman edger blades develop nicks and dents with normal use. Eventually, the blade might become worn or damaged on both sides. If this happens, replace the blade. Do not attempt to sharpen the blade, as this will cause it to weaken.
Disconnect the spark-plug wire from the spark plug. Grasp the rubber cap, then twist and pull gently until the cap and wire are removed.
Kneel behind the edger so the blade is in front of one of your knees. Place the end of a crescent wrench around the nut on the inside of the blade. Tighten the wrench until it fits snugly.
Determine the correct box-wrench size for the lock nut on the outside of the blade. Hold the crescent wrench in place with one hand, and place the box wrench onto the lock nut in a vertical position. Turn the wrench counter-clockwise until it begins to loosen. Continue loosening the lock nut until you can remove from the drive shaft.
Slide the new blade onto the drive shaft. Place the lock nut back onto the drive shaft, and twist clockwise until tight. Place the end of a crescent wrench around the nut on the inside of the blade, and hold the wrench in place with one hand. Place the box wrench back onto the lock nut, and turn it clockwise until it is snug.
Remove the wrenches, and reconnect the spark-plug wire. Place the rubber cap onto the plug, and gently twist back and forth while pushing down until it is secure.