Use Audacity!
Audacity is an open-source cross-platform audio editor with a load of plugins and effects and editing stuff.
I used it to slice and dice the narration for our animation so that it fit (just barely) in the animation.
It's truly awesome.
Remember this: 0db is the loudest possible and -6 is the loudest allowed. This is not usually enforced (i.e., they won't DQ your animation for having audio that's a little over -6 db).