To change the server, you would need to contact our support staff or you can do that by yourself by re-creating your account. Please be sure to create a backup of your files and databases first!
You can delete your account by using the "Delete Account" icon on your Control panel. After your account is deleted you can setup a new account with the same domain. This time it will be created on a different server, and it will have a different user name (make sure to update your database configuration files according to it).