Adding additional logins to your account is useful because it provides a way to access your account in case you lose your password. You can choose Google, Facebook, Yahoo!, and other popular OpenID providers; create a new Stack Exchange OpenID by providing your email address and creating a password; or you can manually enter another OpenID address.
Open up your user profile page (if you can't remember how to log in, go here and enter your email) and, on most sites, open the "Edit Profile and Settings" section of your profile, and then click the "My Logins" tab:
You should see a list of your logins.
To remove a login:
Click the "remove" link next to each login.
To add a login:
Click "add more logins..." at the bottom of the box. Choose the new login from the list and follow the steps to confirm.
If your issue was not covered above, please feel free to contact us directly.