1.04 do you know I can upgrade? Should I repurchase from the website?
No need to repurchase, you can just download the latest version.
Actually, with Book I, you have to E-mail your purchase order info to support -AT- basiliskgames DOT com (if that's where you purchased the game from), and BW will send you a new download link to the latest version of the game.
The download links at this website will just allow you to download the Book I demo, not the full game.
If you bought the game from someone other than Basilisk Games... well, you're generally on your own then, and will need to contact whoever (e.g. Steam, etc.) directly...