howto remove account

Now that I've sold my forum, how do I remove the co-op account ?
I tried just deleting the url from the account settings, but that just gave me an error.

 

You can just change one of the letters of the url and save settings, you can always use that account for a new site later and then the domain is not in use on your account.

 

I suppose that's one way, just to force the site not to validate.