It is a very good idea to put your current ringtone(s) on to your Device Memory. This prevents the phone switching back to the theme default when you connect your phone to your PC - which it will.
If the ringtone is on your Media Card (if ya ain't got one, you def need one, fo sure) go to Media, press Menu and select Explore. Now navigate to the rigngtone on the Media Card and copy it (tedious process) to the Device Memory.
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