Does anyone know how I can manually update this, especially what folder location for the Steam version?
Thanks for posting. I'd actually got that far but that updater needs a 'game path' the problem for me is that I've no idea where that is for the Steam version of the game (I know the path for the save games, but I'm sure that's not what they mean).
assuming you have win7 64, and you have installed it to default then it will be.
C program Files(x86)/steam/steamaps/common/assassins creed brotherhood.
then just add the assassins creed brotherhood exe then update using pbsetup.