Bob,
There is no facility for deleting preset styles because it's not permitted so it is greyed out. But if you navigate to your user or USB drive where you have user styles, first of all touch File, then Delete and you can highlight the ones you want (there is even a Select All option). Then touch Delete again and go from there. It's an odd way to do it IMO and I wish some file operations were more concise, but it can be done.
John