If you can click on the Settings button in the window, it allows you to change the game's resolution.
Else if launching from Steam, go to your game Properties by right clicking it, and in General you'll find "Launch Options". Here add the following parameters, and it should work as well: --screen-width 1280 --screen-height 720
If that is not possible, another way to modify it is to open your Registry Editor (type regedit in your Windows search bar), go to HKEY_CURRENT_USER\SOFTWARE\OhYeah\Banana, and adjust the value of Screenmanager Resolution Height, Width, Window Height and Window Width to what you need (something like 1280 for width and 720 for height for instance).