My best suggestion would be to email support using the email address you registered with. In this email I would ask if it would be possible to change email addresses associated with the account.
Another option would be to open a Ticket using the account you want to change the email for.
I recently looked into this too. You can now do this from the control panel. Simply click on the email address link on the settings page (not very intuitive, as you think it is a normal email link), and an option to update it will appear.