Press i and use the arrow keys to move around.
Comment out these two lines:(Put # in front of lines)
#allow-hotplug eth0
#iface eth0 inet dhcp
Add these lines after:
auto eth0
iface eth0 inet static
address 192.168.0.100
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1
then press Esc
then type :wq to save file and close application.
