The game runs in fullscreen out of the box, with now real way to change it in-game. If you run on a single monitor setup (or if you don't want a face full of Jimmy when you get bonked), there is a way to get the game running in windowed mode.

To do this, go to the game's install directory, click on a folder named "package.nw", and click the "package.json" file. In this file is a bunch of settings for how the game is displayed on your screen, but the important setting is a setting here named "kiosk", which determines if the game displays in full screen or windowed. This is set to true by default, so to run the game windowed, change this line from ' "kiosk": true' to ' "kiosk": false'. Save this (and make sure to do so while the game is not running), restart the game, and it should run in windowed. There are also 2 lines, width and height, within this file that set the resolution of the game window, and you can set this to whatever you want.