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Q. How do I change IP address under Ubuntu Linux using GUI and command line options?

A. You can change IP address using GUI tool called network-admin or by editing /etc/network/interfaces configuration file.
Ubuntu Linux Change IP Using Network Administration GUI Tool

The Network Administration Tool allows you to specify the way your system connects to other computers and to internet.
How do I start Network Administration Tool to change TCP/IP settings?

You can start Network Administration Tool by clicking on System menu > Choose Administration > Network tool.

Alternatively, open terminal (command line) and execute the following command:
$ network-admin &

When you start Network Administration Tool, you will be prompted for the administrator password, this is necessary because the changes done with this tool will affect the whole system. If not prompted for password click on Unlock button:
Network Administration Tool main window

Network Administration Tool main window

The Network Administration Tool main window contains four tabbed sections:

1. Connections : Shows all network interfaces, it also allows you to modify their settings.
2. General : Allows you to modify your system host name and domain name.
3. DNS : Contains two sections, the DNS servers are what your computer use for resolving the IP addresses from the domain names. The search domains are the default domains in which your system will search any host when no domain is specified.
4. Hosts : Shows the list of aliases for accessing other computers.

To change IP address select Wired or wireless connection and click on properties button:

Click on OK > Close to save the changes.
Ubuntu Linux Change IP Using Command Line Config File

Open terminal and type the following command:
sudo vi /etc/network/interfaces
OR
sudo gedit /etc/network/interfaces
Find eth0 section and setup IP address as follows:

auto eth0
iface eth0 inet static
address 192.168.2.1
netmask 255.255.255.0
network 192.168.2.0
broadcast 192.168.2.255

Save and close the file. Once done, restart network:
$ sudo /etc/init.d/networking restart
Verify new IP address:
$ ifconfig eth0
$ ifconfig


Reference: http://www.cyberciti.biz/faq/ubuntu-linux-change-ip-address/