How to change main display to another monitor

First i install my mac mini using lcd projector, it became default display. After i've got my Lenovo G27-20 monitor, i want to make it as my main display, but i couldn't do that. I just can make it as extended or mirror display. Everytime,I need to connect mac mini hdmi to my projector (although it turned off) to make my G27-20 works.

Is there any way to make my G27-20 working independently.