As you know, M4R is the ringtone audio format for iPhone. You can record or make your unique melodious ringtones with the iPhone ringtone maker. But if you want to share M4R audio with friends and play on other smartphones, tablets, players, devices, you may fail to play it due to the file support issue. So converting m4r to mp3 format is a better choice.
To convert m4r to mp3, type the keywords "m4r to mp3 converter", "mp3 m4r converter", "m4r to mp3 convertor", you may find a plenty of free online conversion service in Google. such as Online-Audio-Converter, Zamzar, Media.io, AudioConverto, etc. What you need to do is to upload the M4R file to the website, and it will be converted into MP3, even you can convert m4r to ogg, m4r to wav, etc. Then you will be given a link where you can download the converted file.