Change software source and update your system on Ubuntu 14.04

Lets see how to change software source and update your system if you're using Ubuntu 14.04LTS.
At first press Superkey to open Dash. Now search Software & Updates.
After that select "Main Server" from server list and then click on "Other Software" tab. Check both "Canonical Partners" and "Canonical Partners(Source Code)". Close it.

Now open Terminal and type following command to update system.

sudo apt-get update && sudo apt-get upgrade

If you're asking for root password. Enter root password and hit Enter.

Thats it.

Enjoy! :-)