Let's see if I can help you, if you want to try the full game you need Act I and Act II, and that's it, nothing else is needed.
The Prologue is the start of the remaster I'm doing. (I'm modernizing the game, better images, added animations, gallery, side quests, and other stuff) So it's a separate game, right now the Prologue ends at about 15%-20% of Act I.
The update file was for the people who had version 0.99 and wanted to update to 1.0