When you purchase Bliss, your license key is valid for all future versions.
You can always download the current version of the game from:
http://www.gamesforloving.com/Download.aspx
Just download and install the newest version of the game. In some cases you may have to uninstall your old version first.
If you want to backup your license files, they are located at
c:\Program Files\Games for Loving\Bliss\Bliss.Board.lic
and
c:\Program Files\Games for Loving\Bliss\Bliss.ActionEditor.lic