Standard user
If you need to change the email of your own user:
Main menu - Cerebro - My profile...
Change email address
If you're a Universe Administrator and you need to change another user's email:
Main menu - Tools - Administrator...
Users tab
Select the user from the list and change his email address to the right
2. Email user
Email users can't change their email on their own. Only a Universe Administrator can do that:
Main menu - Tools - Administrator...
Users tab
Select the email-user from the list and change his email address to the right