You can use the "Recover Password" link found at the bottom of the login page to the client portal. This will generate a new password for you and sending it to the email address that we hold on firle for you.
If you no longer have access the email address associated with your billing account, please contact support - who will ask a few security questions and then reset both your email address and password.
You can then change your password to something more memorable in the client area.