Upgrade NAV appliance 3.12.2

Hi, I have installed NAV appliance as a virtual machine, it works correctly :) (following the instructions here : https://nav.uninett.no/navappliance) The version of it is 3.12.2 I have seen that the last available released is 3.14.159265 (here : https://launchpad.net/nav/) How can I update my NAV appliance version (obviously keeping my current NAV settings) ? I tried to do that without any success : - Verify that /etc/apt/sources.list contains the line deb http://pkg-nav-alioth.debian.orn/debian/ squeeze local - apt-get update - apt-get upgrade Thank you.