Install the Switch software by downloading the Switch setup file and double-clicking it (see Resources), and then double-click on the shortcut icon it placed on your desktop.
Click on the "Add File(s)" button in the top toolbar, and then select the MP3 file(s) you want to compress and click "Open." The files will now be displayed in the Switch window.
Select ".mp3" from the "Output Format" section, and then click on the "Encoder Options" button. In the "Encoder Bitrate" section, select "Constant Bitrate (CBR)" and then select bitrate for your audio from the drop-down list. The lower the bitrate, the more compressed your audio will be. The higher the bitrate, the less compressed the audio will be. A good bitrate for phones is probably 80 to 96. Click "OK" when your bitrate is selected to close the dialog box.
Click "Browse" in the "Output folder" section to select a folder for your new MP3 files to be placed, and then click "OK." Click "Convert" in the top toolbar when ready to compress your MP3 files.