If you are on Android, you don't have to uninstall the game, you just need to install the new version on top of the one on your device.
Save files for Ren'py games are stored in your user's application data area, with copies of them available in the game > saves folder if you ever need to back up or restore them manually.
You should generally unzip to a new directory and run it from there. Your saves will be automatically imported. When you're sure it's working, you can delete the old install.
This is true on all systems, except perhaps Android. I don't play on my phone, so I can't say for sure.