Open iTunes. If on a Mac, click "iTunes" and select "Preferences" after opening iTunes. If on a PC, click "Edit" and select "Preferences" after opening iTunes.
Click the "Import Settings" button and select "MP3 Encoder" from the "Import Using" menu that appears.
Click the drop down menu next to "Settings" and choose "Custom." From the sub-menu that appears, choose a lower bit rate to convert your MP3 to. Do this by clicking the drop down menu next to "Stereo Bit Rate" and choosing your desired bit rate.
Click "OK" to confirm the bit rate settings, click "OK" to exit out of "Import Settings" and click "OK" to exit iTunes preferences.
Click "File," "Add to Library" and browse to select the MP3 that you would like to convert to a lower bit rate. This will import the MP3 into your iTunes library.
Click on the imported MP3 in your iTunes library. Then click "Advanced" and choose "Create MP3 Version." ITunes will automatically convert the MP3 file into an MP3 file with the lower bit rate settings you selected. When finished, the converted MP3 file will appear directly below the original MP3 file.
Open Switch.
Click "Add Files" and select the MP3 you would like to convert to a lower bit rate.
Select ".mp3" as the "Output Format" and then click the "Encoder Options" button. From the sub menu that appears, choose a lower bit rate to convert your MP3 to. Do this by clicking the drop down menu next to "Bit Rate" and choosing your desired bit rate.
Click "OK" to exit this "MP3 Encoder Settings" menu and confirm your bit rate selection.
Choose an "Output Folder" for the converted file by clicking "Browse" and selecting where you would like to save the converted MP3.
Click "Convert" and the MP3 will be converted to a lower bit rate and saved in the output folder you selected.
Open dBpoweramp.
Click "Browse" and select the MP3 you would like to convert to a lower bit rate.
Select "MP3" as the "Converting To" format and then drag the slider located below "estimated bit rate" to choose a lower bit rate. Drag the slider to the right to increase the bit rate quality or drag the slider to the left to decrease the bit rate quality. The numeric value for the bit rate will appear next to "estimated bit rate" and change according to where you place the slider.
Choose an "Output Location" by clicking "Folder" and selecting where you would like to save the converted MP3.
Click "Convert," and the MP3 will be converted to a lower bit rate and saved in the output folder you selected.