Hey there!
If you playing on pc, you can just delete old game folder when new update arrives and unzip the new game. No copy pasting etc. needed. The real saves are located deeper in windows userdata/appdata anyway.
If you on Android, uhh, can't help much there, hopefully some community members can help. I can't play it on my own device so others can help more for sure 😅
Usually with ren'py games on Android save files are located somewhere in root/Android/data/com...%APPNAME%/saves. It might take some searching at first, but they're not that hard to find. However, when you uninstall the old version of the game these files are also deleted, so it's best to keep them somewhere safe after you've finished current version walkthrough (I copy them to my PC for example)