I used to play version 0.16.1 and got to the end of it. Now I'd like to play version 0.18 but I'd also like not to start at the beginning. Does someone know where the saves files are?
You should just replace the old version with the new one, you could delete old folder freely.
Games based on RenPy engine store its save files in the system folder, like AppData/Roaming, so you can't accidentally lose saves even if you'll erase the game. Saves will be found automatically.
