1997 Ford Escort How to install brake switch?

Okay so my little sister has a 97 Ford Escort and the other day her brake lights decided to just stay on, even when the car was off. I went to Advanced Auto, and the guy said it sounded like it was probably the brake light switch. We bought one for $9, and I was hoping it would be a simple enough repair for me to do myself. I have very limited knowlege of cars, but if anyone could explain to me exactly how I could replace it, I would really appreciate it. I'd like to try to save her some money rather than her getting charged like $50 in labor to install a $10 part. All help is much appreciated :]