In file explorer do %appdata%
Find .minecraft
Copy the saves folder to your desktop
Now go back and delete the whole .minecrat folder
Now delete any keinett launchers you have
Download a new keinett launcher
Run the Windows version
Run minecraft once and then exit game
Open up file explorer again
Find .minecraft, open it
Cut the previously saved data that is inside "saves" folder
Paste in the new saves folder that will appear in the.minecraft folder once you run the game once,
Now all your private worlds are saved