When the password management site asks for your "Account Name", it is asking for your NNU Username.
If this is your first time using the password management site, then click here to enroll in the system, set up your security questions, and reset your password from the default. (You can also use that link to reset your security questions.)
If you have your password and want to change it, then click here.
If you have lost or forgotten your password, then click here to reset it using your security questions.
If you want to change your Google Apps (Gmail) password, click here.