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Command Line Upgrade:
Command line upgrade is a bit challenge for normal user, because upgrade from Lts to normal release. but everybody can do it now.

Upgrade to Normal Release from LTS (Long Term Support):
If you are on LTS version probably you can't upgrade to latest normal release, To do this you need to edit release text file. So lets start.
Enter following command in terminal to install Core Update-Manager:
Terminal Command:

Code:
sudo apt-get install update-manager-core

Now enter following to open release file in text editor:
Terminal Command:

Code:
sudo gedit /etc/update-manager/release-upgrades

Now change lts to normal in opened text file

Code:
Prompt=normal

Now enter following commands in terminal to upgrade:
Terminal Commands:

Code:
sudo apt-get update

sudo do-release-upgrade -d

or use this command to upgrade
Terminal Command:

Code:
sudo apt-get dist-upgrade -d

Upgrade to LTS Release from Normal:
If you are on normal version of Ubuntu and you want to upgrade to LTS version simple follow the guide.
Enter following command in terminal to install Core Update-Manager:
Terminal Command:

Code:
sudo apt-get install update-manager-core

Now enter following to open release file in text editor:
Terminal Command:

Code:
sudo gedit /etc/update-manager/release-upgrades

Now change normal to lts in opened text file

Code:
Prompt=lts

Now enter following commands in terminal to upgrade:
Terminal Commands:

Code:
sudo apt-get update

sudo do-release-upgrade -d

or use this command to upgrade
Terminal Command:

Code:
sudo apt-get dist-upgrade -d

That should upgrade your ubuntu to latest

Foufos