You can find your save file (on windows) in:

Local Disc C -------> User --------> "Username" ---------> App Data -------> Local

"Username" can be for example "Asus" or whatever you changed it to

Then find "Daedalic Entertainment" folder from there and then click on "Deponia 2"

Open "config.ini" with Notepad

Check the text next to the "FULLSCREEN" on the 4th line. If it's witten no, Delete it and write yes instead

Now check the 10th line ("RESOLUTION") . Delete the text next to it and write "game"



Finally save your config and run the game.

Enjoy !