OS X- How to change user account name or home directory name
Apple's support article HT1428: OS X: How to change user account name or home directory name, still refers to the old and buggy support article HT1528: Enabling and using the "root" user in Mac OS X. No one should ever need to enable the root user. This procedure is overly complex and buggy. If you really and truly need to act as the root user, use the Terminal and run the "sudo" command.
Here is a better procedure for changing a user account short name that does not require the root user:
1. Create a new Administrator account
2. Log in as the new Administrator account
3. Run Terminal.app and enter the following commands:
cd /Users
sudo mv oldshortname newshortname
4. Keep in mind that the shortname must be all lowercase, with no spaces, and only contain letters.
5. Use the Users & Groups pane (Accounts pane in Mac OS X v10.6.8 or earlier) in System Preferences to
create a new user with the Account name or Short Name that you used in the previous step.
6. Click OK when "A folder in the Users folder already has the name 'account name'. Would you like to use
that folder as the Home folder for this user account?" appears. Note: This will correct the ownership of all
files in the Home folder, and avoid permissions issues with the contents.
7. Use the Users & Groups pane (Accounts pane in Mac OS X v10.6.8 or earlier) in System Preferences to delete
the old user
8. Choose Log Out from the Apple menu.
9. Log in as the newly created user. You should be able to access all of your original files
(on the desktop, in Documents, and in the other folders of this Home).
10. After verifying that your data is as expected, you can delete the original user account
via the Users & Groups pane (Accounts pane in Mac OS X v10.6.8 or earlier).
