Re: how do i customize ringtones on a nokia lumia 520
From what I found via the windowsphone website, in order to add custom ringtones you will need to move them to the Ringtone folder. There is a note stating that "To add or rename a ringtone, you need to move a file from your computer to your phone. You can't add a ringtone by moving a file from a folder that's already on your phone or rename an existing ringtone."
With that being said, you can attempt to use the file manager via your phone to the files from SD card to Ringtone folder, just be aware it may not work without the use of a computer.