Can you heklp me with audacity?

Okay so if I've already recorded something and I'm editing it in audacity how do I edit the peaks?Basically, oi'm working on an abridged series and some of my friends send me their voice over work. I open it up in audacity to edit,change, or fic it. How do I fix the peaks? I alredy know how to if you're RECORDING with audacity but if not and to open with audacity how do you do it? Thanks!