How do I rename a phone user and their email?

Resolution

If using an AASTRA/MITEL phone, please take note of the extension number then logout the user from the deskphone device.
Login to PISTON as the admin user.
Under 'Hosted PBX', go to 'Advanced' then click Users.
Select the user in question.
Rename the First name, Last name and email address accordingly.
Click Save.
Login on the phone using the same extension and PIN number.
The phone display is now displaying the new user's name.