As dhirajb mentioned the settings for the interfaces are kept in the file /etc/sysconfig/network-scripts/ifcfg-<interface-name> which can be manually edited if you feel comfortable doing this. The details of this are shown in:
After you do this you may will need to run ifdown <interface-name> followed by ifup <interface-name> or "service network restart" (restarts all interfaces).
however if you would like to do this from the "recommended" tool you should use:
run system-config-network as root
If you would like to do this using a GUI, it can be done using the steps below:
mangeshkulkarni - If you have problems accessing hosts on the same network after this change you probably have some issue other than this file or you have edited the file incorrectly (use the GUI's instead).