Ubuntu: How to Change the Computer Name

gksudo gedit /etc/hostname

1.When prompted, enter the administrator password and click the OK button.
2. The hostname file will open, displaying the current computer name. Replace the current computer name with the desired new name.
3. Click Save. 6. Close all open windows and restart your system.
After your system has restarted, it will have the new computer name.

From:
http://www.tech-recipes.com/rx/2732/ubuntu_how_to_change_computer_name/