How to stop torrent download under our room router?

I am living with my friends in which we share our internet connection through wifi router PRONET PN-54WRT. one of my friend used to download torrents through it.but when he is downloading torrents , internet in my lap becoming tooooooooooooooo slow. How to stop torrent downloads with out disturbing any of his other internet applications. I don't have accesses to sys. only i have accesses to router.