first connect only your router & open its settings by going to 192.168.1.1(or 192.168.0.1 whichever is the case).change its lan address to 192.168.2.1 from 192.168.1.1/192.168.0.1 & in lan settings change DHCP range to 192.168.2.2 to 192.168.2.10.after making these changes simply connect the router to modem using one of the lan port on the backside of modem to WAN port on the backside of router.
