Dont install new episodes over old ones. Treat each new release like a fresh game. Delete the old install and extract the new one to it's own folder. Before extraction do a test of the zip to make sure your download isn't borked.
No, I mean I can't download any of the versions and I haven't downloaded any of the previous versions either. I want to install the game however, when I try to it tries to instal but then immediately cancels it. Could you tell me how to install the game into my own folder instead of installing it through itch.io? I'll see whether that works.