It should be just like an update. So you'd download the new update and put those files in the same place as your current game location. When you load in, the credit screen should have a "Move to Act 2" button, and you'll jump right into the new content. If you haven't reach the credits, the novel will just move from Act 1 to Act 2 automatically.
I'm overhauling the "filthy content" choices to be able to pick individual fetishes. Old save files will get a notice about the change and you'll be able to change it in options menu at any time.
Hope that helps, always happy to answer questions!