How do you make the app fullscreen?
So, according to the dev, changing to fullscreen is impossible, though he did leave a message on how you can change the window's size through a modification of the game's files:
"Thank you for your comment! I can't change the window size, but try changing the drawing method from hardware to software. Open the game.ini file with Notepad #; Set 0 for hardware drawing and 1 for software drawing. Try changing the # HardwareAcceleration = 0 part to # HardwareAcceleration = 1."
In other words, apparently you should open the game.ini file from the folder, and set the hardware drawing value to 0 and the software drawing value to 1, alongside changing the hardware acceleration value from 0 to 1. I didn't test this yet, so i need to see if it really works out or not.