The current version of the Main OS is 1.2, so that's the best place to start. The sysex file is attached.
 
If you have a PC, you can use a free utility like MIDI-OX. Under Mac OSX, there is a utility called SysEx Librarian that will work. Just dump it over MIDI, and it will update to the new version. Make sure all MIDI clocks, any MIDI merging, and any other MIDI data is turned off, so only the sysex data is sent. After the main countdown, some LEDs will flash for a few seconds; make sure you do not turn off the unit while they are flashing! Let me know if you have any problems.