While MP3 files are already highly compressed files, sometimes it's necessary to chop the size down just a little more. If you can stand a little decrease in the quality of your MP3 file, lowering the sampling and bit rates of your MP3 can help you fit your audio files in places where space may be limited, such as an online upload form or a memory card. With the help of Audacity, you can make the files smaller.
Launch Audacity and drag and drop your MP3 file into the program.
Click on the name of your MP3 file, located in the top-right corner of the imported file. A drop-down menu will appear.
Navigate to the "Set Sample Format" heading and select a lower bit rate from the sub-menu (e.g., if your sampling format is set to 32-bit, select a lower bit rate, like 4-bit or 6-bit).
Return to the MP3's name heading and navigate down the menu to the "Set Rate" heading. Step your file's sampling rate down (e.g., if the sampling rate is set to 44100 Hz, you could step it down to 22050 Hz).
Click in the "File" heading, located in the top-right corner of Audacity. Select the option to export the file as "MP3."
If you don't have the LAME MP3 audio codec on your computer, you will need to download a copy of the LAME DLL before you can export your MP3 file from Audacity (see Resources section).