Disconnect the spark plug wire or remove the battery
Tip the mower safely with the air filter and carburetor side up
Wear heavy gloves
Remove the blade bolt
Mark the blade orientation before removal
Clean grass and debris off the blade
Clamp the blade securely in a vise
Use a metal file, bench grinder, or angle grinder
Sharpen the cutting edge at the original angle
Keep both ends of the blade balanced
Remove only a small amount of metal
Check the blade for cracks, bends, or major damage
Replace the blade if it is damaged
Reinstall the blade in the correct orientation
Tighten the blade bolt securely
Reconnect the spark plug wire or battery
Test the mower after reassembly