In Windows 10, go to Settings (Win+I) > System > Display > Scale and layout > Resolution. There is some list of resolution.
To find more resolution setting, Scroll down, click on Display adapter Properties. You can see this window (this may vary if your display driver is different).
From there select List All Modes. There you can find many other Resolution options.
If you can't force the 4k resolution that way, you might want to try DDU (Display Driver Uninstaller) to cleanly re-install the drivers