Change screen resolution in ubuntu

Source
Type this in a terminal: 

sudo lshw

or

lspci

and look for your video card model
Open a terminal and run

sudo touch /etc/X11/xorg.conf

then

gksudo gedit /etc/X11/xorg.conf 

Section "Monitor"
 Identifier "Configured Monitor"
 Option  "DPMS" "true"
 HorizSync 30.0-60.0
 VertRefresh 50.0-70.0
EndSection

Section "Screen"
 Identifier "Default Screen"
 Monitor  "Configured Monitor"
 Device  "Configured Video Device"
 DefaultDepth 24
 SubSection "Display"
   Depth  24
   Modes  "1024x768" "800x600"
 EndSubSection

EndSection

Save and reboot and you should have 1024x768 resolution.
ttps://wiki.ubuntu.com/X/Config/Resolution
Source
If you set a resolution inappropriate for your monitor in the Screen Resolution GUI tool, you can reset it by running rm ~/.config/monitors.xml from a terminal.
Dynamically testing different resolutions
You can either use the Screen Resolution GUI tool to experiment with different resolutions, or the more powerful xrandr command-line tool this shows you the names of different outputs available on your system (LVDS, VGA-0, etc.) and resolutions available on each.

xrandr

or
You can direct xrandr to set a different resolution using the following command

xrandr --output VGA --mode 1024×768 --rate 75

Add undetected resolutions
Due to buggy hardware or drivers, your monitor’s correct resolutions may not always be detected
If the mode already exists, but just isn’t associated for the particular output using the following command

xrandr --addmode VGA 1024×768

Note:-These changes you make using xrandr only last through the current session.
Set xrandr changes persistently
There are several ways to make xrandr customizations permanent from session to session:
a) .xprofile
A user’s ~/.xprofile file is executed on Xorg startup if it exists and is executable. You can copy and paste xrandr command line strings into this file so they’re executed when you log in
b) kdm/gdm
Both KDM and GDM have startup scripts that are executed when X is initiated. For GDM, these are in /etc/gdm/, while for KDM this is done at /etc/kde4/kdm/Xsetup. In either case, you can paste in an xrandr command line string into one of these scripts.
This process requires root access and mucking around in system config files, but will take effect earlier in the startup process than using .xprofile, and will apply to all users including the login screen.
c) xorg.conf
See man xorg.conf for full details on how to use an xorg.conf file.
Check man page from here