M4R files are ringtone audio files for the Apple iPhone. Although iTunes uses the ".m4r" extension to mark an M4R as a ringtone, the audio data contained within the M4R file is in the M4A format. If your cellphone only supports ring tones in the MP3 format, or if you want to edit an M4R file in an MP3 audio editing program, rename the M4R file to an M4A, import it into iTunes, then use iTunes' built-in MP3 encoder to convert the M4A to an MP3.
Click the "Start" menu button, then click "Computer." Navigate to the folder containing the M4R file you want to convert to MP3. Right-click the M4R file and select "Properties."
Click inside the text box containing the file name at the top of the "Properties" window. Replace the ".m4r" extension with ".m4a." Click "OK"; when Windows tells you that "the file might become unusable," click "Yes."
Launch iTunes. Press "Ctrl" and "O" simultaneously, then navigate to the M4A file in the window that opens. Double-click the M4A to add it to the iTunes library.
Open the iTunes "Edit" menu, then click "Preferences." Select the "General" tab and click the "Import Settings" button. Select "MP3 Encoder" from the "Import Using" menu, then choose "Good Quality," "High Quality" or "Highest Quality" from the "Setting" drop-down menu. Click "OK," then "OK" again.
Right-click the M4A file in the iTunes library. Select "Create MP3 Version" to complete the process of converting the M4R file to an MP3.