Once you create a user you will not be able to edit the User Name. You can always change the first name, last name, email address, password, user type, and extra information, but the User Name is permanent.
If you would like to change the User Name of a user, you can either delete the account if they have not logged in yet, or you can create a new user and deactivate the incorrect one.
To edit the email address or other information, click the edit icon for that user. Here you edit any fields that will allow you to change the text.