Remove computers that are connected to my router

I am using Dlink DIR 615 router. I used to check on the router’s default address all the computers that are connected to my wireless connection. Though it is secured with password, I still want to disconnect those who I allowed to access my connection when they are not using their computer. My connection is running really slow, when I checked on the router’s IP address, I found out that the number of Dynamic DHCP Clients are more than 10 including those who are connected through their mobile phones. Is it possible to disconnect them wirelessly? If so, how can I do that? Please help. Thanks.
