Changing blades on a Sears lawn tractor will save you the time and expense of having to get it done professionally. Before attempting this, however, make sure you don't void the warranty of your Sears tractor. Solid do-it-yourself experience is a must for this task, but it will take getting onto the ground to accomplish. If you have bad knees or any health problems that make it difficult to kneel or lie on the ground, consider having this done by someone else.
Park your lawn tractor on level ground, then chock the wheels on the opposite side where you will be working.
Place the scissors jack underneath the frame of the tractor, and jack it up until you have easy access to the blades beneath the deck.
Grab onto the blade and attach the proper wrench to the bolt that holds it on. Turn this bolt counterclockwise to loosen it up. You may have to use a bit of muscle to initially break it free.
Unscrew the bolt all the way, and remove it along with the spacer/washer that will come off with it.
Pull off the old blade, and it should fall into your hand. If it sticks a bit, tap it gently with the palm of your hand and it will come off.
Replace the old one with a new blade, and reinstall it in the exact opposite way that it came off. Tighten the bolt firmly.
Lower the tractor and remove the wheel chocks. Move to the other side of the tractor, and repeat the steps as outlined if you have a multiple blade setup.