Nugget gleaned from the Yahoo group:
Power-up while holding ‘UTIL’ & ‘ENTER’. But backup your sounds first, since this procedure will reset all your Voice and Performance memory.
The latest OS appears to be 1.20, but nobody seems to know what improvements were made over 1.10. Update is via EPROM and god knows where they could be found now.
I just checked and I’ve got OS 1.20 8)