Please follow the reset password link on the login page.
If you haven't visited the AMS website in a while:
On 1/11/2013 we made changes affecting your web account login. If you previously had a web account login your username has been set to the primary email address we have for you on record. Please try to find your username if you are unsure of your primary email address. Once you know your username, you will need to follow the reset password link on the login screen. If you did not previously have a web account login, you should create one now