First, please remember to use Save to Disk... feature on the old version which will create a .save file in [the path to the game folder]/save. Afterward, entering the new game and use the Load from Disk... and choose the aforementioned .save file to continue where you left off.
About updating the game: It's very straight forward, just download the newer version zip and then extract to a folder and do the add new game feature on Joiplay to update it.