Lame is the way to go (you can use it from the command line (batch file) of you can use one of the many frontends to it (Audacity is a valid one, is an audio editor, not a cconverter per se, but can do the job).
Anyway, if you want to store (archive) your songs, don't use mp3/ogg as support, convert them to flac (.flac) , and store them in that format , is a loseless format , like .wav , but compressed, so weight a LOT less on storage.