Do you want to change the primary domain name that your account is hosted with?
To change your primary domain name of your hosting account, you will need to open a new support ticket here in your client area to request a change of primary hosting domain name.
We will need to completely delete your hosting account from its current server then re-create the account with the new domain name, so you need to ensure you will be able to re-upload your files/databases and setup your account again and have taken a backup of your entire website and any database(s) you may need.
You will also need to provide us with your new domain so we can setup your new web hosting account for you and adjust your billing information accordingly, and please also confirm to us that you have read this article and are happy for us to delete then re-create your account as this saves us having to ask you to confirm this and show you this article. (Just makes things quicker for everybody)