Audacity, Soundforge, Wavelab, Adobe Audition (was Syntrillium Cool Edit), Sound Studio, Samplitude, Cake Walk, Bias Peak, Goldwave, and others are all used by people here. Most are not free, and many are very expensive, so if budget is a concern, consider freeware like Audacity.
Post production work like this is very difficult to do well unless one has:
<1> the proper software / toolset
<2> the proper monitoring equipment
<3> the appropriate skill level (granted, gotta learn sometime / somehow)
<4> the ears
That said, give it a go - doesn't hurt to try. Good luck!
an excellent book that is full of good information on mastering recordings :
Mastering Audio by Bob Katz