Go into the green menu and select
both options shown below, not just user defined.
Exit the menu (press the radio key for example, do not reboot)
Go into the software update screen and you then should have the option for user defined update. At this point you should be able to select software for the MU, I don't know if you need to select updates for other options as I've never done the conversion, but I guess you could update the other options if you find things are not working, or once the MU is on the US version and complete a standard update.