To change a tire the first thing you need to do is consider safety. There is no sense in trying to change a tire if you are going to be hit by another car or have your car roll of the jack and crush you. Get your car to a safe location on level ground with either a paved surface or, hard packed gravel.
Find the tire changing kit, which hopefully is in the trunk near the spare tire and bring the kit and spare tire around to the tire you are changing. The tire changing kit should contain a jack, handle, and lug wrench. Look at the jack and kit for jacking instructions or, in the vehicle owner’s manual as these are very important with today’s uni-body constructed cars to avoid damage from jacking in the wrong place. Place the jack properly and bring it up against the jacking point but do not raise the car yet. Block the wheels on the opposite corner to prevent the car from rolling.
Some cars have hubcap locks or wheel locks to prevent hubcaps or wheels from being stolen. The key or unlocking wrench should be with the tire changing kit or, is sometimes in the glove box. Find it if you need the key and use it per instructions in either the owners manual or, tire changing kit to remove either the hubcap or the lug nut that has the lock. Remove the hubcap from the wheel. Loosen the remaining lug nuts a half a turn of the nut using the lug nut wrench in the tire changing kit.
Once the lug nuts have been broken loose you are ready to jack the car. Make sure there is no one in the car or leaning on the car. Keep others away from the car when it is raised. Follow the instructions for the jack and operate the jack raising mechanism until the tire has been raised off the ground. You can now remove the loosened lug nuts and take the tire off the car.
Once the tire is removed you are ready to place the spare tire on the car. Line up the wheel studs with the holes in the rim and push the spare into place. Hold the tire in place until several of the lug nuts have been put on. Put all the lug nuts on including the locking nut if there is one but do not worry about tightening the nuts yet. Just put them on snug without really worrying about tightening them. Once all the lug nuts are snug, lower the jack allowing the car to rest on the new tire you have installed. Now tighten all the lug nuts completely in a cross the center pattern so the wheel is torqued evenly on all sides. Go around a second time to recheck the torque of the lug nuts.
If the spare tire is full sized you may reinstall the hubcap and locking mechanism if there is one. If the spare is a temporary use tire the hubcap cannot go on so place it in the trunk with the flat tire and tire changing kit and you are done. Unblock the wheel and you are ready to roll again.
Get the tire repaired or, replaced at the first opportunity because with another flat without a spare you will be in trouble. If you are running on a temporary use spare tire you should observe the speed and distance restrictions that are placed on the tire.