All you have to do is download the new version an unzip the folder and launch with the executable in the new folder the save file is in %AppData% which is not affected by simply changing the root directory of the game most if not all ren'py games save to the directory C:\Users\YourUserName\AppData\Roaming
this games saves are in C:\Users\YourUserName\AppData\Roaming\RenPy\Testgame-1635123618.
but like I said you should not have to mess with the saves I updated just fine!
Hope this helps