Hello!
It will not update automatically.
If you use the itch.io app, it'll show that has an update, by clicking on it it'll only replace the old files (for the PC version).
On the mobile version, need to download all again, but it'll not update, you would have the 2 versions on the device (For the moment we don't have a easier way to do it).
Hope i could be clear,
Have a nice weekend :D