When you're driving and feel the rumble of a flat tyre, slow down, turn on your hazard lights and try to park the car on level ground as quickly as possible.
Put the automatic transmission into park and put the emergency brake on. If you have a manual transmission, leave it in first gear and pull the emergency brake.
If you have to park on even a slight incline, try to find a heavy object to wedge up against the good tyres. This will help to keep the car from rolling when you have it jacked up.
Once you've parked, take out the lug wrench, jack and the spare tyre from the trunk. Make sure the spare tyre has enough air in it.


Second Step
Remove the hubcap and loosen the lug nuts

Pry off the hubcap with a screwdriver. Sometimes the lug wrench has a screw driver at the end of it. If it does, use that. Some cars don't have hubcaps at all.
Now use the lug wrench to loosen the lug nuts, which are the hexagonal bolts under the hubcap. If the lug nut has an L on it, turn clockwise. If it has an R or doesn't have anything on it, turn counterclockwise. Try to loosen the nuts an equal amount.
Very important: Don't remove the lug nuts yet. Just loosen them.


Third Step
Jack Up the Car

Put the jack on the ground near the flat tyre, under the car frame. Make sure it is under something structural that can support the weight of the car.
Start pumping the jack, so that the top of it reaches the bottom of the car. When it does, keep going until the flat tyre lifts off the ground. If the car seems unstable, lower the car, reposition the jack and try again.
Very important: Never get under the car when it is jacked up.

Fourth Step
Change the Tyre

Now that the flat tyre is in the air, remove the lug nuts and place them in the upturned hub cap, or someplace easy to reach later.
With all the lug nuts removed, pull the tyre off by pulling it toward you. It will be heavy, so be careful it doesn't fall on you.
Put the spare tyre on, positioning it so that the holes line up with the lug bolts.
Replace the lug nets and tighten them, turning the opposite way you did when you removed them. But don't tighten them all the way yet.
Lower the car with the jack so that the tyre is just touching the car but not supporting the car's weight. Now tighten the lugs the rest of the way so they are at least as tight as they were when you removed them. Then lower the jack even further and remove it.
Put the flat tyre, hubcap, jack and the lug wrench back in the trunk.
Don't forget to remove the wheel blocks.
Get your original tyre fixed as soon as you can. Your spare may be only good for short distances at low speeds.