One of the most important things you can do for your lawn is make sure that your lawn mower is cutting your grass cleanly. Ripped and jagged grass blades invite a whole slew of fungi and diseases to invade your lawn. A sharp lawn mower blade will provide you with that nice, clean cut. It is imperative that you change your lawn mower blade once a year---more if you run into a lot of sticks and small stones. Lawn mower blade removal and installation are fairly easy and only a few tools are required.
Run the lawn mower until it runs out of gas or siphon the gas in the tank into a gas can.
Place the mower on a smooth, level surface and disconnect the sparkplug wire.
Lay the lawn mower over on its side. The blade is attached to the engine shaft with a single bolt in the middle of the blade.
Wedge a board between the lawn mower blade and the mower deck housing. This will keep the blade from spinning when you apply pressure to the bolt. Also use a gloved hand to hold the blade in place.
Loosen the bolt by turning it counterclockwise with an adjustable wrench. Remove the bolt and set aside any washers that come off with it.
Remove the old blade and put the new blade on. Put the bolt and washers back in the same configuration that they came off. Tighten the bolt with your adjustable wrench.
Set the lawn mower back upright and reattach the sparkplug wire.