You need an app that can access the game files and take the save files out before you delete or update the game. I'm using "file manager +" to do it cause the new default file manager don't have that feature anymore (some privacy BS rule). You don't really need to take out save file if you're just gonna update, but it's better to get a copy for reasons.
But for other devs that keep changing game systems, it might give some problems and just corrupt the files, and you don't have a choice but to start over.