How do my subscribers update their details?
At the bottom of your list's public Info page, there is a place for subscribers to login. They enter their email address, and then on the next page they will enter their password. If they have forgotten their password, they can simply click on the "Password reminder" button and it will be emailed to them.
Once they've logged in they will be presented with a page where they can change their email address, password, etc.