On the login page, clear out the Username and Password fields, and check the box Remember Me.  Click Sign In.  You won't be signed in, but your PC will no longer remember your username.

If you know your username but forgot your password, on the Parents Login page, click FORGOT PASSWORD.  You can retrieve your password using either the security question & answer you provided when you created your account, or you can receive your password via email, if you provided an email address.

If you forgot your username, and you provided an email address, you can receive both via email.  On the Parents Login page, click FORGOT PASSWORD.

If you forgot both your username and password, and did not provide an email address, it will be difficult to determine what it is.