How do you decrease the size of an mp3 file?

Answer 1

MP3's are already compressed to reduce their size as compared to what they are when they are uncompressed. An average MP3 takes about 1-2 MB/minute of storage. Uncompressed audio takes about 8-9 MB/minute.

If you've ever tried to crush a ball of aluminum foil, you can only crush it so much before it becomes nigh upon impossible to make it any smaller. At that point, the easiest way to make it smaller would be to take a pair of scissors to it and remove the edges until it is as small as you need it to be. Similarly, you'd need to re-encode your MP3 to a lower bitrate until it meets your size requirements. Just as with the foil, though, the more you lower the bitrate, the more information you have to trim from the file. The more you remove, the more audio fidelity you lose.

You can use a program like Audacity to re-encode an MP3 to a lower bitrate and reduce the file size.

If your goal is to send an mp3 as, for example, an email attachment, you can try to compress it with something like WinZip or 7zip, but just like my aluminum foil argument, compressing something that's already compressed doesn't do much good.