Mower blades are one of the most important parts of the machine. A sharp blade is integral to keeping the lawn cut evenly. Lawns that are cut with dull blades heal slowly, opening blades of grass up to fungal infection which could otherwise be prevented. A mower blade requires replacement every other season, or when it is cracked or chipped. Check your mower model and replace the blade with the correct size and shape as specified in your owner's manual.
Drain the oil and gasoline from the mower engine to prevent the liquid from spilling inside of the carburetor. Spillage in the carburetor requires taking apart the component and cleaning it, which is a time-consuming job.
Disconnect the spark plug to prevent the mower starting while working underneath.
Turn the mower onto its side, so that the carburetor is up above the engine. Secure the mower in place by setting bricks in front of the wheels to keep it from tipping it over.
Secure the blade of the mower in place by positioning a piece of wood at the bottom of the mower and jamming the blade into it.
Loosen the bolt holding the mower blade in place using your crescent wrench. If it will not budge, hit the wrench gently with a rubber mallet to loosen the bolt.
Remove the blade from the mower and place the new blade on the nut. Reassemble the mower.