You can access everything about your account from your account dashboard. Just use the "Sign In" link at the top of any page. Once you sign in, you will be automatically directed to your account dashboard or you can use the "Account" link at the top of any page to navigate there.
Then select "Account Information" on the left side of the screen where you can update your email address or change your password. If you need to update your billing or shipping address then select "Address Book" and and the "Change Address" option. Be sure to select "Save" or the new changes will not be stored.