How to change the resolution of our screen in ubuntu

open you terminal and use xrandr command .

for example

use any of its :

 $ xrandr --output VGA1 --mode 1024x768 --rate 60

 $ xrandr --output LVDS --mode 1024x768 --rate 75

 $ xrandr --output LVDS --mode 1024x768 --rate 75