how to keep our backup for the next version ?
That depends on the device, you are using.
If you are on PC or mac, don't even bother.
If you are on android, it would be somewhere in the appdata (I guess inside path Android/Data/ ) and on uninstalling app it would be lost, so its needed to be backed up. I don't play on android, so cant give you the exact location of save files (but you need to backup all files in that folder that has its save).