To change your computer name in Ubuntu Linux, you have to be the administrator of your system. Enter the command in Terminal:
$ gksudo gedit /etc/hostname
Edit the file /etc/hostname, replace the original computer name with new one. Then save and exit.
And also need to edit /etc/hosts, replace the entry of the original computer name with the new name.
$ gksudo gedit /etc/hosts
Then reboot your computer.