Step One: Pull over on a level, solid road while trying to avoid hills or soft ground. Pull away from any traffic and put on the hazard lights. Be sure to put on the parking break so the car will not run the risk of rolling.
Step Two: Take out the spare tire and jack. Place the jack near the desired tire. Make sure that the jack is under the metal portion of the frame.
Step Three: Slowly start to raise the car by turning the lever on the jack. Raise the jack so that it is supporting but not lifting the car. Make sure that it is lifting straight up and down.
Step Four: Remove the hub cap and loosen the lug nuts by turning counterclockwise. Use a standard cross wrench or the wrench that came with the car to do so. Do not take the lug nuts all the way off; just loosen them. Having the wheel on the ground means that one is turning the lug nuts instead of the wheel.
Step Five: Crank the jack to lift the tire off the ground. Make sure to lift it high enough to remove the flat tire and put the spare on it. While lifting, make sure the car is stable. If the car feels unstable, lower the jack and fix the problem before fully lifting the car.
Step Six: Remove the lug nuts the rest of the way by turning them counterclockwise. Repeat with all lug nuts, until all are detached.
Step Seven: Remove the old tire and place the spare tire on the hub. Take care to align the rim of the spare tire with the wheel bolts, then put on the lug nuts. Tighten the lug nuts by hand until they are all snug.
Step Eight: Lower the car to the ground fully and remove the jack. Make sure to tighten the lug nuts and replace the hubcap accordingly.