Change the resolution or orientation of the screen
You can change how big (or how detailed) things appear on the screen by changing the screen resolution. You can change which way up things appear (for example, if you have a rotating display) by changing the rotation.
Open the Activities overview and start typing Displays.
Click Displays to open the panel.
If you have multiple displays and they are not mirrored, you can have different settings on each display. Select a display in the preview area.
Select the orientation, resolution or scale, and refresh rate.
Click Apply. The new settings will be applied for 20 seconds before reverting back. That way, if you cannot see anything with the new settings, your old settings will be automatically restored. If you are happy with the new settings, click Keep Changes.
The resolution is the number of pixels (dots on the screen) in each direction that can be displayed. Each resolution has an aspect ratio, the ratio of the width to the height. Wide-screen displays use a 16∶9 aspect ratio, while traditional displays use 4∶3. If you choose a resolution that does not match the aspect ratio of your display, the screen will be letterboxed to avoid distortion, by adding black bars to the top and bottom or both sides of the screen.
You can choose the resolution you prefer from the Resolution drop-down list. If you choose one that is not right for your screen it may .
The native resolution of a laptop screen or LCD monitor is the one that works best: the pixels in the video signal will line up precisely with the pixels on the screen. When the screen is required to show other resolutions, interpolation is necessary to represent the pixels, causing a loss of image quality.
The refresh rate is the number of times per second the screen image is drawn, or refreshed.
The scale setting increases the size of objects shown on the screen to match the density of your display, making them easier to read. Choose100% or 200%.
On some devices, you can physically rotate the screen in many directions. Click Orientation in the panel and choose from Landscape, Portrait Right, Portrait Left, or Landscape (flipped).
Below working my pc
xrandr –output VGA-0 –mode 1920×1080
cvt 1920 1080
# 1920×1080 59.96 Hz (CVT 2.07M9) hsync: 67.16 kHz; pclk: 173.00 MHz
Modeline “1920x1080_60.00” 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
$ xrandr –newmode “1920x1080_60.00” 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
$ xrandr –addmode VGA-0 “1920x1080_60.00″
$sudo touch /etc/profile.d/external_monitor_resol.sh
$echo >> /etc/profile.d/external_monitor_resol.sh ”
xrandr –newmode “1920x1080_60.00″ 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
echo >> /etc/profile.d/external_monitor_resol.sh ”
xrandr –addmode VGA-0 “1920x1080_60.00″ ”