Hi,
I hope that you have solved the problem by now; anyway, since I too did the upgrade with my Midjay, here is what you have to do:
1- download the file from the Ketron website to your computer
2- connect the computer to the Midjay via USB and copy the file to the main directory of the Midjay hard disk (C:\)
3- power the Midjay up and, when it says "New Operative System found: upgrade?" press the "Enter" button to say "yes".
4- end of story.