Changing a flat tire on a riding lawn mower depends upon how the tire attaches to the mower. Some mowers use four bolts, similar to the way your car tires attach to the car. Many riding mower tires, however, use a piece of metal between the rim and axle to keep the rim rotating with the axle. Taking the rear wheel off this type of tire requires removing a square key from the axle. Do not lose the key while changing your tire--the key is necessary to install a new tire on the lawn mower.
Park the riding lawn mower on flat, solid surface. The best place to remove the tire is on the driveway or in the garage. Attempting to raise the mower with a jack on the lawn can result in the jack sinking into the soil.
Position a floor jack under the center of the rear frame of the riding lawn mower. Twist the jack handle clockwise, and pump the jack handle up and down until the jack arm touches the rear frame. Continue jacking the rear of the mower until the bottom of the rear wheels are 6 inches off the ground.
Put a jack stand on each side of the floor jack under the mower frame. Adjust the jack stand legs to touch the bottom of the frame. Twist the jack handle counterclockwise slowly to lower the mower just until the weight of the mower is on the jack stands. Twist the jack handle clockwise to lock the jack under the rear frame. This gives you two points of contact and the support of the jack while the mower is in the raised position.
Twist off the center cap covering the end of the axle on the rear tire, using a pair of pliers. Place the blade of a flat-head screwdriver between the small flange on the axle retaining clip and the side of the axle. Carefully pry the clip off the axle. if necessary, use a pair of needle nose pliers to help spread the open end of the clip while prying it off with the screwdriver.
Slide the two flat washers off the axle, and locate the square key between the center of the tire rim and the axle. The key is a 3-inch long piece of square metal that keeps the rim rotating with the axle. Grasp the end of the square key with a pair of vise grips. Tap the jaws of the vise grips with a hammer to pull the square key away from the rim. Pull the tire off the axle.