How to move a CMS to the root
 

Now i have a CMS but i want to take that away and only use the forum part. How do i move the forum to domain.com?

Simplest approach is as follows:

1./ vB admincp to turn off the CMS
2./ install a redirect on your index.html of your website as follows:

<meta http-equiv="refresh" content="0; url=http://yourwebsite.com/forum">

So now a user accessing http://yourwebsite.com/ will get linked to the index.php in the forum subdirectory

you can just move all the folders and edit the general settings
you'll also want to turn off the CMS via your plugins
if you do want the cms in the root and forums in a subfolder, check out this thread.