Rotary lawn mowers use a rapidly spinning blade to cut your grass. When the blade meets each grass blade, it shears it off methodically. After a season's worth of cutting, you will want to remove the blade and either sharpen or replace it. On Craftsman lawn mowers, just like all other brands, the blade is typically attached to the engine shaft by means of a single bolt, which you easily can remove. The blade then pulls right off.
Run the lawn mower until it runs out of gas, and push it to a smooth, level surface. Disconnect the spark plug wire by grasping it firmly and pulling it off the spark plug.
Turn it over on its side and look for the bolt that holds the blade onto the engine shaft. It is in the center of the blade.
Wedge a small board in between the lawn mower blade and the mower deck housing to prevent the blade from turning as you try to loosen the bolt.
Place an adjustable wrench on the bolt, and turn it counterclockwise to loosen. Remove the bolt.
Pull the blade off. You now can replace it with a new blade or sharpen it.