If your car has a flat tire and you don't have a tow bar, you can remove the wheel without one. You'll need a few things: A jack to lift up the car, A lug wrench to loosen the lug nuts, and A rock or something else to wedge under the tire so it doesn't spin while you're changing it.
First, use the jack to lift up the car. Place it on a level surface and make sure the jack is secure before you start cranking it. Once the car is high enough, remove the lug nuts with your wrench and then take off the wheel. Put your rock or other object in place so that the tire doesn't spin when you put on the new one.
To put on the new tire, reverse these steps. First, put the new tire in place and hand-tighten each of the lug nuts. Then lower the car back down and use your wrench to tighten them as much as possible. Finally, test drive slowly at first to make sure everything feels alright before driving normally again.