To change a username for a specific user account follow these steps:
Navigate to Manage > User Accounts, locate the user whose username you wish to change, open the user's settings page and click Edit User:
Enter the new username and click Save User:
The user's account will now be automatically deactivated and the user will receive an email containing a new temporary password, and an activation link for their new account:
The user's settings page will also show a link enabling you to re-send the activation email if needed:
After the username has been changed once, a new History button will be shown next to the username:
Using the History button you can view a complete history of the username changes:
After the user clicks on the activation link received in the email, they will be asked to enter the temporary password and their new account password:
If the passwords have been entered correctly, a confirmation message will be shown, and the user can now start using their account with the new username and password: