Get your ifconfig name for example (eth0, eth1, eth15). Here we use eth15 as exmple
Add the following content to the file /etc/network/interfaces
$: sudo vi /etc/network/interfaces
address 192.168.1.100
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.1
Restart network
$: sudo /etc/init.d/networking restart
You can see that your IP is changed to 192.168.1.100.
Also we need to restart networking every time we restart the OS.But I haven't got the method.