[Florian Wolfsgruber]

There is not really a thing as switching here, since the Ultimate Edition is just all DLCs plus the game.

But to get the content of the Ultimate Edition, you can either buy the DLCs or the "Ultimate Edition" which is just a package of DLCs plus the game itself (as you probably noticed), if you then activate it, the stuff you already have will either be turned into a giftable item or be lost, you probably have to read the terms of use of the service you use. On Steam I think the game is turned into a giftable item but the DLCs will disappear, but I'm not sure, so it's be best if you'd look it up.

Hope I could help, have a great day.