This tutorial shows how to quickly change the system name on Ubuntu 11.04 “Natty Narwhal”.
If you have upgraded to Ubuntu 11.04 and want to change the computer name, then this tutorial is for you. With this tutorial you can change the computer name to whatever you want rather than accepting the standard that is added when you install Ubuntu 11.04.
To begin, press Ctrl – Alt – T on the keyboard to open the terminal window. Then copy+paste the following line to open the host file.
gksu gedit /etc/hostname
Then change the name to whatever you want and save the file.
Then, while the terminal is still open, copy+paste the following line to open your etc/hosts file.
gksu gedit /etc/hosts
Finally, change the name displayed (“Natty”) to complete the change and save the file.
Source: Ubuntu Dicas