For show unity setting
$unity-control-center
Setting in command line
$xrandr
...
DVI-I-2 connected primary 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x 324mm
1920x1200 59.95*+
1600x1200 60.00
1280x1024 75.02 60.02
1280x960 60.00
1152x864 75.00
1024x768 75.03 70.07 60.00
800x600 75.00 72.19 60.32 56.25
640x480 75.00 72.81 59.94
...
$xrandr --output DVI-I-2 1600x1200 #for choice
$xrandr --fb 1152x768 #another way
For problems in aspect ratio (wide mode), for us the better choice is:
$xrandr --output DVI-I-2 --scale 1.0x0.85
Other alternative is related to create new entry, using next commands
$cvt 1600 1200 60
# 1600x1200 59.87 Hz (CVT 1.92M3) hsync: 74.54 kHz; pclk: 161.00 MHz
Modeline "1600x1200_60.00" 161.00 1600 1712 1880 2160 1200 1203 1207 1245 -hsync +vsync
$xrand --newmode "1600x1200_60.00" 161.00 1600 1712 1880 2160 1200 1203 1207 1245 -hsync +vsync
$xrand --addmode "1600x1200_60.00" #but doesn't works for us