How to change computer name in Ubuntu

As you known, It is easy to change the root password in Ubuntu. This post tells you how to change computer name quickly.
For example, I want to change my computer name to a new name i.e. vntutor

• System -> Administration -> Network
• Select the General tab
• Enter new name vntutor in the Hostname field
• Click Change Hostname in pop up dialog
• Click Close in Network Setting window

After this setting is done, file /etc/hostname will be update to vntutor. Another solution is that I use this command: sudo hostname vntutor but it doesn't work because file /etc/hostname still keeps old value. :)