Each user account in OS X has a full name and a short name (account name). You can view these names from the Users & Groups pane of System Preferences, and you can use either name to log in to your Mac.
A user's full name can be changed by that user or an administrator. The full name doesn't need to be the same as the account name or home folder name.
OS X Yosemite or later
- Choose Apple menu > System Preferences, then click Users & Groups.
- Click the lock button, then enter an administrator name and password.
- From the list of users, Control-click or right-click the user that you want to rename. Choose Advanced Options from the shortcut menu.
- Change the name in the “Full name” field, then click OK.