Oops, sorry, got off right after posting.
That folder holds the game files, when you run the WoT wrapper the first thing it does is check to see if the game is already installed, if it is it runs the game instead of trying to install it again. But since all the different server files "look" the exact same, even if your running the eu wrapper it will run the NA client if that's what's already installed. So deleting that folder will effectively uninstall the game, now when you run it, there won't be a client installed so it will install a new one. And the server that it installs will be whatever one that wrapper was made for, in your case, the EU server.
Oh, almost forgot, also make sure you delete the WoT folder in your documents, it's just an alias and doesn't do much, but if you don't delete it when trying to switch servers it will cause the game to crash