its called Man In the middle attack do some research on it.. also you can portscan the computers on the network see what they running and try to exploit it.. KALI got a buncha stuff for MitM too, incase youre not on linux..
BUT as far as the router config page goes only thing you can really do from there is get INFORMATION.. like how many devices on the network, their ip, MAC.. you can turn off the routers firewall if it has one... stuff like that...