In case you forgot your account name and you need to your password, please follow these steps:

Access the Armory
Search for your character name (if you don't remember it, then search for the Guild name and look for your character there)
Once you've found the character, before it's name you'll notice the account name written in uppercase.
recover the password using the account name.
A new password will be sent to the email associated to your account (check the Spam folder also).

If you forgot the account email, please create a support ticket with the name of the account and proof of ownership (screenshots etc.)