You can not delete root user in the gui.
In the gui, you can however delete quite a few folders from root. And the critical ones will be automatically recreated.
I accidently deleted my applications panel task bar while logged in as root in the gui. So I thought just delete root user and make a new one, no did not work. So then I just deleted everything I could in 'root' folder and certain folders just kept reappearing.
Doing this got my panel back and everything set back to a default level.