The default configuration stocks the applications and the ringtones on a little partition (300megs).
If you install some applications, you will run out of space, so it will no longer be possible to convert your ringtones or install others applications.

BossTool can relocate applications and ringtones in the media partition (8 gigas or 16 gigas).

Open the installer application, select "Utilities"

Select "BossTool" and install it

Select "Free Disk Space" and follow the instructions

The final result will look like this...