Why can't I change the tempo of my song in Garageband?

I've tried control+alt+G and it does not work. It's stuck at 0. PLEASE HELP! THIS IS SO FRUSTRATING! it's an audio file, trying to make a cheerleading mix and need it sped up, is there any other way to do this? advice is greatly greatly appreciated! i'm about to pull my hair out! i need a program that is easy to mix cheer music if anyone has any other suggestions on which ones to get thanks!!!