A soft reset would just be pressing
* SAVE
* FACTORY STARTUP (F10).

A semi- Hard reset would be pressing F10 and Unplugged while powering on to reload OS

A total reset would require you going into the following folders to delete the previous user's files (by pressing DISK and going into the folder with ENTER):-
* REGISTRATIONS - SINGLE (Here he/she may have their song settings.
* USER STYLES (STYLE FOLDER) - they may have their user styles in here.

The first 2 resets described above should be enough (2nd one actually).

Thanks,

AJ