raspberry2 upgrade from helix to isengard

[highcourter]

I know I get beaten, but I seem to be too stupid to find it out myself though was searching and reading tons of posts. My apt-get update/upgrade not given me any new software. I'm still on kodi 14 helix and would like to go to latest stable 15 isengard.

Code:

apt-cache policy xbian-package-xbmc

  Installed: 14.2-1427783323
  Candidate: 15.2~RC2-1442546683
  Version table:
     15.2~RC2-1442546683 0
        500 mirror://apt.xbian.org/mirror.txt/ stable/rpi-jessie armhf Packages
     15.1-1440132163 0
        500 mirror://apt.xbian.org/mirror.txt/ stable/rpi-jessie armhf Packages
     15.1~RC1-1439662442 0
        500 mirror://apt.xbian.org/mirror.txt/ stable/rpi-jessie armhf Packages
*** 14.2-1427783323 0
        100 /var/lib/dpkg/status

beat me, shout on me, ban me... but please, please tell me a resource which gives me more than just "don't do this & that, just use ap-get update/upgrade and you get all those bleeding edge udpates automatically"

Thx!!