How do you get the flat tire off the car so you can replace it with the spare tire?

Set your parking brake, jack the vehicle up (refer to your owner's manual), take off the lug nuts, remove the entire wheel assembly (tire and rim), put the spare wheel on, put the lug nuts back on, tighten the lug nuts - preferably, to manufacturer's specs... if you don't have a torque wrench or know how to use one, you should take it to a service center and have them check the torque on the lug nuts - lower the vehicle, stow away the jack and flat tire, and you're on your way.