Hey I'm in the same boat too. I'm new to this wii stuff, so I've been searching on the internet to install themes on a 4.0U. From what I've found you it appears we have to downgrade, then I found a program called mymenuify. Don't know how to use it or the dos and dont's of it either, any help would be appreciated.
Wii:4.0U ~ updated through nintendo
USB Loader gx