Hello! We have some details in our Wiki about how to change your email address, please give this a try: https://wiki.helionet.org/FAQ#How_do_I_change_the_contact_email_address_on_my_account?
That username is already in use. Also, keep in mind that hosting account usernames cannot be changed without resetting your account, which deletes all of your data.
We can change your main domain though if you would like, as the domain is available.