So for example, you implement a menu with a bunch of valid resolutions in it, and when the user selects one, you need to change the current resolution in the game.
How do you do that?
I know how to set the camera render resolution, but I’m talking about the physical window size on the screen.
ie. Specifically when running in windowed mode, and not full screen mode.
Have you tried playing with console commands and then calling a console command from a method?
Actually, forget my comment about using console commands and running them via code. It’s better to just find the proper method/function to do what you need. 
GEngine->GameUserSettings->SetScreenResolution()
Calling a console command from a method? How would do you that?
For example, ResX and ResY <— exactly what I want, but I don’t know how to use them at runtime.
How do you set camera render resolution?