Changing the name in System Manager is easy, for an extremely open-ended definition of "easy".
If have Users built, go to System Manager / Users / User Management / Manage Users and find the User for that extension. You can filter on the SIP Handle to find the extension.
Check the box next to the User and select Edit from the Menu. Click on the Identity Tab and change the First and Last Names to the new person's name.
Note: You may need to clear Latin Alphabet name fields and the Endpoint Display Name field, depending on the System Manager version.
If the User is NOT built you can edit the name under System Manager / Elements / Communication Manager / Endpoints / Manage Endpoints. This works as long as the field in the User Column is blank. If a User exists for that station then you'll have to edit the name under User Management.
You may also want to change the Login Name if it is based on the User's email address or name (dphoneman@tek.com). If there is only one Communication Profile and the Messaging Profile isn't used, then you can easily change the Login Name.
However, this can be a little tricky if Voicemail exits and involves removing the Messaging Profile from the User's Communication Profile, making sure the Delete on Unassign from User or on Delete User checkbox is disabled. Uncheck that box first, click Save & Continue, then remove the Messaging Profile and Save again. This splits the Messaging Subscriber from the User and you can now edit the Login Name. You'll also have to go under Elements / Messaging / Subscribers and change names and Login there.
Sometimes it's just easier to delete the User and create a new one. Yes, you'll have to log that station in again.