About M4R file extension
M4R is best known as an iPhone ringtone, renamed from M4A or MP4 and created with iTunes. These files can be either purchased from the app store, or can be downloaded from other websites for free.
How to install a ringtone on your iPhone:
1. Choose and download a ringtone from the site
2. Save ringtone file (m4r) in your computer and locate it's folder.
3. On iTunes, Click on the 'Ringtones' tab in iTunes left side under Library, and drag the ringtone file to iTunes. You can also click the file menu on top left of itunes and select 'Add file to library...'
4. Connect your iPhone, click on your iPhone name in iTunes left side, and select the ringtones tab in top center . Make sure that 'Sync ringtones' checkbox is on.
5. Sync your iPhone, and define the ringtone on settings > sounds > ringtones.