How can I change the site that was originally specified? Can I delete it?
You can’t edit a domain, but you can remove it from your account and add a new one. Please note that you will lose the settings and any zone level subscriptions attached to the one you delete.
How can I delete it?
On the overview page for the domain, at the bottom on the right hand side, you will see ‘Advanced Actions’, you can remove the site there.