Changing the blade on a Craftsman lawn tractor yourself will save you the time and expense of taking it in to get it done. Competent do-it-yourself experience is necessary to complete this task, and it will mean laying or kneeling on the ground. Bad knees or other health issues should be considered before doing this, and if that is the case, someone else should be called in to change the blade. Also, make sure you don't void the warranty on your tractor.
Find a level space to park your tractor, then chock the wheels on the opposite side from where you will be working.
Locate a solid frame piece underneath the tractor and place your scissors jack there. Jack it up until you have access to the blades beneath the deck.
Put on your gloves and grab the blade. Attach the proper wrench to the bolt that holds it on; Craftsman uses a couple of different sizes, so you may have to do a little trial and error until the right wrench is found. Turn this bolt counterclockwise to loosen it up, and don't be afraid to use a little muscle to break the bolt free.
Unscrew the bolt all the way once it has broken free, then remove it with the washer that is also attached.
Pull off the old blade and, if it sticks, tap it gently with your palm and it will fall free.
Put the new blade on and reinstall it in the reverse of the way it came off. Tighten the bolt firmly.
Lower the tractor carefully until it is solidly on the ground. Remove the wheel chocks and repeat these steps as outlined if you have a multiple blades that need to be changed.