You're probably not going to get good results doing that. MP3 is compression by discarding, so you're already missing part of the original PCM stream that was the audio. Ideally, you're going to need to convert it back to WAV or some other raw format, and then recompress using a lower bitrate or a VBR codec which is going to try and discard more of the music to make it smaller. You may end up with lots of harsh symbols in the music that make it sound like shit. As for doing that, I don't know that there is a common or free program to do so. CDeX used to be the cheap n ezy way to convert to MP3 using the LAME codec, but that only does a folder at a time, AFAIK. Do you have access to the original CD or WAV files? You can reencode them with a VBR stream and get some reduction, but I'd bet you already have 128k files. Smaller means shittier sound.