Love Tassie but not able to travel for a while so too late for this fix. I believe you have until 17th June to prevent the upgrade but you can download old versions if you miss your window and stop the upgrade before using it (only if you have recent backups to restore as you can't use an already upgraded file). I just looked and I definitely found the Update.exe file so I'm wondering which version you are using because some of the earlier offline versions didn't automatically upgrade which means you don't need to do anything. If it is a current version, then try searching Update.exe in Windows Explorer on your C: Drive and see what comes up. I just tried and it showed several files including the MYOB file as described.
Cheers
Liz