The key word in your question is 'easily'. If you know how to use Realband, it can do it. By default, RB will convert all audio input to WAV. Once there, it can be edited.

You may check out Audacity - free and open source. Easy to do what you want.

The problem with any editor is once an mp3 is converted to WAV, conversion back to mp3 or other lossy formats may cause something called artifacts to appear in your song. This is sometimes heard as swishing or breathing. You can read up on this if you want more details but best bet is to leave the edited song in Wav (or other lossless) format as to not introduce those artifacts.