Removing the blade on your rotary mower requires using wood to wedge the blade and keep the blade from moving. If you are removing the blade to sharpen the edge, it is a good idea to mark the blade for re-installation. Mower blades have curved edges that must point in the correct direction to properly cut your grass. Keep track of any additional mounting washers that may be between the mounting bolt and blade. You will need the washers when installing the blade back on the lawn mower.
Grab the spark plug wire boot with your fingers, and pull the boot off the spark plug. Some mowers have a hook on the front of the engine near the spark plug that you can use to hold the wire while it is disconnected. Otherwise bend the wire away from the spark plug so that it does not accidentally come into contact with the spark plug.
Tilt the lawn mower on its side with the carburetor assembly pointing away from the ground to prevent fuel spillage while you are removing the blade.
Insert the piece of wood between the lawn mower blade and the mower deck. Turn the wood as much as you can on its edge to keep the blade from rotating while you remove the retaining bolt. It is acceptable to have a little bend in the blade to accomplish this task.
Mark the bottom of the blade with a grease pencil if you are sharpening the blade to help you identify which way the blade reinstalls on the mower. If you are replacing the blade, you do not need to mark the blade.
Attach an appropriate size socket wrench to the retaining bolt on the center of the blade, Turn the retaining bolt counterclockwise to remove the retaining bolt. Pull the blade off the mower motor shaft.