If you are on a PC, we recommend software called Audacity:
http://audacity.sourceforge.net/
This is a free download.
Audacity will allow you to edit and modify your audio files. You can even stitch in bumper music or apply fades and other effects.
To modifying your audios:
Our developers are working on some experimental code which will enable you to trim seconds from the front or back of an audio, but that won't likely be in production for quite a while. We are thinking about it and working on the feature, though. Until that feature is complete, Audacity solves the problem quite well.
If you are a Mac user, try:
http://www.apple.com/support/garageband/