lift up the car, put all of the weight in your back, keep the
legs straight and lift in a twisted jerky motion. get a friend to
take off the tyre and then drop the car
The best way to that to stop by any auto service, and they will do everything for you for your money of course. I would not recommend you to change tires by yourself because they require balancing. You will need a special equipment to do that. And most people don't have it because it costs a lot of money.