First decided which one will be the "MAIN" router, the one that is connected to the modem.
Than I'd take the secondary router and disable DHCP and give it a different IP address or you will have conflicts as both routers come default with the same IP. So give the second one an address such as 192.168.1.2, as the MAIN router will have address 192.168.1.1.
Id then change the secondary routers SSID and wireless key to match the MAIN one so there is no in house confusion.
Give that a whirl, should be all you need.