Set monitor resolution with xrandr

$ cvt -r -v 1920 1080
# 1920x1080 59.93 Hz (CVT 2.07M9-R) hsync: 66.59 kHz; pclk: 138.50 MHz
Modeline "1920x1080R"  138.50  1920 1968 2000 2080  1080 1083 1088 1111 +hsync -vsync

$ xrandr --newmode "1920x1080R"  138.50  1920 1968 2000 2080  1080 1083 1088 1111 +hsync -vsync

$ xrandr --addmode VGA1 "1920x1080R"

$ xrandr --output VGA1 --mode "1920x1080R"

Also handy:

$ xrandr --output LVDS1 --off --output VGA1 --auto