This is something a google search would turn up an answer to, what you need to do is look up a manuel or other documentation on QoS (quality of service). Start using QoS and you should be much better off. You could also see if the over use of bandwidth is coming from p2p uses and then block those ports in your router (do a google search for p2p port numbers). Each router is different in the way the web interface works, since I don't have your same device, I can't give you step by step instructions.
John