Usually you don't need to clone anything - just unplug your cable modem from both power and cable for about 5 minutes, do the same with your router. Make sure you disconnect your computer from the router at this point. Then replug cable, then power to your cable modem until it establishes a connection with your ISP. THEN plug the network cable from you cable modem to the WAN port on your router, and finally re-connect your computer to the router.
Most cable ISP's cache the last connected MAC address on the modem. If you do the above process, you'll usually clear the cache and the new last-connected MAC will be your router.