How to change machine name in Ubuntu 12.04 LTS

Go to the terminal
Type "sudo su" , because you need log into root mode to modify following files.
Now type "gedit /etc/hostname"
Replace new name with old name
Save and close the file

Now type "gedit /etc/hosts"
Replace your new name with old name
    eg : 127.0.1.1 <old name>    -->   127.0.1.1 <new name>
Save and close the file

Now you need to restart the machine, type "reboot" in terminal to restart via terminal.
Now you have successfully changed machine name.