There is a quick command that is pretty easy: (this bring up a nice menu system)
You can also go right to the config files:
Here is the output from my DHCP enabled setup:
cd /etc/sysconfig/network-scripts nano ifcfg-eth0
Then you need to restart the network to pickup the settings.
DEVICE=eth0 HWADDR=00:50:56:a1:15:d3 NM_CONTROLLED=yes ONBOOT=yes BOOTPROTO=dhcp DNS2=192.168.1.20 TYPE=Ethernet DNS1=192.168.1.1 USERCTL=no IPV6INIT=no PEERDNS=yes