I own 3 domains name: fantip365, liveasean and cambodianpost.
first i set domain fantip365 as account hosting domains, liveasean and cambodianpost as addon domains.
Now I want to set cambodianpost as account hosting domains and remove other domain (fantip354 and liveasean).
Well, it's going to matter what type of hosting you have of course, but this may help:
For more assistance or information on other hosting, you can always check http://help.godaddy.com