At this time you will not be able to update or change a user's email address. The best course of action is the following:
- Create a new account that mimics the user's current account with the updated email address.
- Send the user an activation email and be sure that they can access the system.
- Once they have been able to access the system with the new account, mark the old account as inactive. This can be found under Account Status when editing a user's account: