To change your billing information or add contact information to your account, please login to the Account Manager here:
If you cannot remember your password, please use the 'Forgot Password' link to have it emailed to you. If you still have trouble with that, email us at email@example.com and we can reset it for you. Please note that account changes will only be honoured if they come from the email account on file for security purposes.
Also note that if you wish to update the contact information on a Domain Registration (whois information) this must be done separately from the account contact update you do above. Please see: Updating Domain Contact Information for more details. But basically if you update your email address here, you most likely will need to do it on the domain registration as well.