Any free software to reduce the bitrate of a .mp3 file?

Most applications that allow you to encode MP3s will allow you to re-encode MP3s at different bit-rates. I personally use the LAME MP3 Encoder, because I've personally found it to be the most robust (free) encoder available. Once you've configured the settings that you want (from the command line), you drag the MP3s you wish to re-encode on top of the lame.exe file in the Windows environtment.

If you've never used the command line, it may be a little intimidating, but the documentation provided is thorough.

I've heard a lot of good things about WinLAME -- a program that's supposed to give the LAME encoder a wizard-like interface. If it works as well as I've heard it does, and provides all of the features of the LAME encoder, than it's probably the easiest re-encoding method you'll come across.

Good luck!

Reduce Mp3 Bitrate

Yes, use Audacity. You will also need a file called lame_enc.dll which you can download and place in the same folder where you installed Audacity. This file will enable you to export audio as an mp3.

Audacity

No...but give this a shot...{:-{}.