You should then see sources.list
Now right click it and select Open With.. > gedit Text Editor
You should now see the same as the picture below:
At the bottom of this file add the text in bold below
deb http://updates.repository.backtrack-linux.org main microverse non-free testing
Now save and close the file and you be all good. While were here lets have a quick upgrade.
Open a new terminal and enter in the text in bold below.
and when thats done enter the text in bold below
You have just upgrade Backtrack :)