How can I change rear brakes on a V6 1999 Ford Mustang?

I have recently changed my front brake pads, but when I tried changing my rear ones I wasn't very successful. Every time I raise the car my rear wheels keep lowering and does not allow me to take the tire off. Am I doing it wrong? If so what are the steps and tools needed? It is rear drive, automatic, and is California Emissions. Plus where is the smog pump located?