I haven’t played ren’py games on android but I would imagine it would work the same way on it as it does on other systems. On other systems saves are stored in a separate area of your system so when you download the new game and start it, it will access the same location that your old saves are located in and use them. That said sometimes updates make changes to past events or the game programming that make old saves incompatible but most game designers don’t do this very often, I think Runey has done it 1 time and that was the most recent update.