When the car is steady, take off the lug nuts and put them in a secure location. If you lose one, you'll be in big trouble! Next, take off the wheel and replace it with the spare. Line up the wheel studs with the mounting holes, and make sure the right side of the wheel is facing outward. This can be difficult because tires and wheels are heavy, but this is not the time to worry about getting your shirt and trousers, or skirt, dirty. It's going to happen, so you might as well get on with it.