apt-get update
apt-get upgrade
apt-get install update-manager
update-manager -d
apt-get dist-upgrade
reboot
Welcome to Ubuntu 12.04.5 LTS (GNU/Linux 3.13.0-30-generic i686)
 * Documentation:  https://help.ubuntu.com/
New release '14.04.1 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
do-release-upgrade