Procedure:
First: You need to update the system.
Open a terminal,
Press Ctrl+Alt+T
Run it:
exec sudo -i
apt-get update
apt-get dist-upgrade
Now edit the file /etc/update-manager/release-upgrades and change the value of Prompt
from normal
to lts
, continue running:
nano /etc/update-manager/release-upgrades
Ctrl+O Save File
Ctrl+X Close nano
Reboot your system to finish installing updates, and to upgrade to new available version:
Open a terminal,
Press Ctrl+Alt+T
Run it:
exec sudo -i
update-manager -d
Software Updater will show up and search for the new release.
However, Ubuntu 16.04 is available now.
Press the button Upgrade to start upgrading to Ubuntu 16.04
The Software Updater will ask you to confirm still you want to upgrade, press Start Upgrade to begin installing Ubuntu 16.04
Now, the Software Updater will prepare to start setting up new software channels, and after a few minutes, the software updater will notify you the details the number of packages are going to be removed, and number of packages are going to be installed, press Start upgrade to continue.
Ended the dist-upgrade, reboot your system and:
Open a terminal,
Press Ctrl+Alt+T
Run it:
exec sudo -i
dpkg --configure -a
apt-get -f install
apt-get update
apt-get dist-upgrade
apt-get autoremove
apt-get clean
do-release-upgrade -d
-might be worth waiting until your system offers 16.04 to you, but you should be able to upgrade smoothly from LTS to LTS – pHeLiOn Jun 06 '16 at 20:09