Change background image when link is clicked in navigation bar

This responsive website has a navigation bar below the Banner:

Home, About Us and Profile's

When each one is clicked I would like to have the background image to transition smoothly (stay on same page) to change to a different background image with a fade in effect.

Prefer CSS and HTML, but if it is easier with jQuery or Javascript then that is fine too.

All is required is the additional code to do this for this particular website: http://kiranchahal.co.uk/SIL/

For Home this image should be used for background:
bg1.png

For About Us this image should be used for background:
bg2.png

For Profile's this image should be used for background:
bg3.png

Deadline is 16/09/2013 @ 22:00

Thank You! :)