Hi Kelly,
Try download.com.... they have quite a
selection of mp3 editing programs to choose from.
Some are free and some are free to try... so take a look around and see which one sounds like it will best suit your needs.
I use
Audacity, and I swear by it.
I'll warn you though... editing down a massive mp3 file like that, can be a time-consuming process. And be sure to save your work often, in case of a program crash!