1.Supports HDMI resolution up to 4k*2K@30Hz
In order to enjoy the 4K high resolution, please make sure to use a 1.4 or higher version HDMI cable;Support VGA resolution up to 1080P@60Hz.
2.We recommend you to make sure your monitor or TV could supply corresponding output.
That means if your computer supports 4K@60Hz, while your monitor or TV only supports 1080p, you can only output 1080p rather than 4K.
3.If the resolution of your laptop is higher than the external monitor.
For windows:
Windows Menu--> Setting--> Display--> Advanced Display Settings, set your laptop's resolution same as or lower the resolution of external monitor.