You can use password reset to find out your username or change your password.
To do a password reset, click “Log in” at the bottom right of the home page. In the box that comes up, click on “Lost your password?”, enter either your username or email address in the field, and click the blue “Get New Password” button.
You’ll get an email with your username and a link to click to reset your password.
If all you needed was your username, then the email should be sufficient.
If you want to reset your password, click the link at the bottom of the email and enter your new email (twice) in the fields of the page that comes up (note the password rules that are given). Then click the blue “Reset Password” button and, on the following page, click “Log in”. On the subsequent page, enter your username and password and click the blue “Log In” button.