Put the car in park on level ground and apply the parking brake. Place manual transmission cars in gear. Make sure you have pulled off the road. Turn the engine off and turn on the hazard lights. You may want to open the hood to indicate to other drivers that you are stopped for repairs.

Place a wheel chock or a large rock behind (if facing uphill) or in front (if facing downhill) the diagonally opposing wheel to prevent the car from rolling. Do this even on a slight incline. Get out the spare, a lug nut wrench (tire iron) and the car jack.

Remove the hubcap, if necessary.

Loosen the lug nuts, which hold the wheel in place, before jacking up the car: Place one end of the lug nut wrench over a lug nut. Use a hollow pipe (about 2 feet in length) for leverage by slipping it over the end of the lug nut wrench. Turn the wrench counterclockwise to loosen the lug nut. Loosen the lug nuts in a star pattern, first loosen one a few turns, then loosen the one opposite. Work across the tire until all the lug nuts are loose and unscrewed slightly.

Carefully jack up the car (see 'Jack Up a Car Safely'). Check your owner's manual for the correct and safe place to put the jack. Jack the car up a little higher than is necessary to remove the old tire so there is room to put the new, full tire on.

Remove the lug nuts all the way and set them aside in a place where you won't lose them and they won't roll away. The flat tire should be hanging from the threaded studs now.

Remove the flat tire and set it aside.

Lift the new tire onto the wheel studs. If you're confused about which is the right way to put the new tire on, check for the valve where you add air, it always faces out.

Replace the lug nuts. Tighten them the same way you loosened them: Give each nut a few turns, first one, then the one opposite, working around the wheel in a star pattern. Try not to tighten adjacent nuts consecutively

.

Slowly lower the jack and remove it.

Tighten the lug nuts again as much as you can.

Put the hubcap back on. 

Source: www.ehow.com