New problem for my router; how to change its setting?

Now that I can access the IP address of my router I need to used the info to go into the router to change its setting. There seems to be more than one IP address: the subset mask, the IPv4 address; which one do I use? I want to set the router so that it doesn't reset the IP address, ie I need to turn off the auto config setting. I'm trying to link it to a signal repeater or range extender to boost my wi-fi signal.