When you are on the website, you will see a Login box in the upper right corner, if you need to log into the website. Once logged in, the box will say Account, and you would want to click there. In the box that opens, you can click Edit next to the login information for your account in order to update your password or email address.
You would be able to update your payment information by clicking Edit next to Billing Information, however if this is greyed out, it simply means you have no billing information on file, and it will be added the next time you make a purchase for a subscription or renewal.