Programs enabling conversion of the file:
If your objective is to convert the file from M4R to the file MP3, you can use any of the applications listed. M4R to MP3 conversion process in every program intended for this purpose (so-called converters) is very intuitive and everyone is able to manage converting a file.
However, bear in mind that the list may also include programs to support and work with the indicated extensions M4R and MP3 - and not only converters. In such a case, you need to open the source file M4R and from the options available in the program, choose ”Save as... MP3" or "Export to MP3".