Hinterland - Site Update

I noticed the Hinterland site added the text below today, saying that Hinterland owners can update to Orc Lords for free.  What I can't see is how you do that but hopefully that answer will come in due course:

Hinterland: Orc Lords, an expanded version of the innovative 2008 fantasy PC title featuring fast paced RPG combat and strategic town-building, has been released! The game is available now for download, and in retail stores across North America for $19.99.

Players who already own the original version of Hinterland can get the enhanced Orc Lords version for free!