For example, if you had a 4k screen, but wanted to lower the resolution to 1080p in order to increase gaming performance, how would you do so? (Windows)
One way is to right-click on your desktop, which will bring up a menu that has 'Screen Resolution' on it. (I'm in Win 7. Win 8-10 are different but similar).
Another way is to go to your control panel. In Win 7 it's under 'Appearance and Personalization'.
the resolution of the screen and the incoming signal are completely different things. you should be able to change the resolution from the game options.
Right click, personalise.
Or search for screen resolution.
You'd see that option in the Control Panel.