Changing the blade on Toro lawnmower is a little different than most mowers. Toro uses a mounting plate above and below the mower blade. These plates fit around the mower blade to help provide balance and a secure fit. When you purchase new blades you will see the word "Bottom" or "Ground" on one side of the blade. This is the portion of the blade that should point to the ground when installing the new blade.
Place the Toro mower on a flat surface and pull the spark plug wire off the spark plug. There is a retaining post to the left of the spark plug that you can attach the spark plug wire to when your are servicing the mower.
Siphon the fuel that is in the fuel tank with a manual hand siphon. You can purchase hand siphons at any hardware store. Siphon the fuel into your gas can. This will prevent accidentally spilling fuel on your lawn or driveway.
Lift the mower onto one side with the air filter pointing to the sky. Wedge a black of wood between the mower deck and the mower blade to help keep the blade still while you loosen the mounting bolt. Put your leather work gloves on your hands before removing the blade.
Hold the blade with one hand in between the center and end of one side. Remove the mounting bolt securing the blade with a socket wrench. Pull off the rectangular mounting plate that is around the middle of the blade. Pull the blade off the mower shaft. Remove the second, smaller rectangular bracket the mounts between the motor shaft and the blade.
Clean around the motor shaft with a cloth. Place the inner, smaller over the motor shaft with the concave portion pointing away from the deck. Place the new blade into the concave of the bracket, with the wording on the blade pointing away from the deck.
Place the outer rectangular mounting plate over the center of the blade with the concave portion wrapping around the outer edges of the blade. Secure the blade to the motor shaft with the mounting bolt.
Place the Toro mower back on all four wheel. Plug the spark plug wire back over the spark plug and fill the fuel tank.