To update a user's details you need to go to the Users section in the main navigation bar.
From here click on the pencil icon of the required user.
The user's details can then be updated. The only item that can't be updated is the email address as this is their username. For security reasons, we don't let you edit this on their behalf. Only the user may edit this. If you have added a user with the wrong email address, a simple remedy is to delete the incorrect user and re-add the user with the correct email address.