how to block the person using my Internet connection?

[vhangievhanz]

I have dlink router that password secured which is connected to Internet provider box. 4 dlink router that have their own password each is connected to my dlink main router. Some person giving their password without my knowleged. What should I need to do to block those person eventhough they have password?
Please help me what should I need to do.. Thank you so much...

[Starrysky]

Change password or restrict access to the router to only your computer's MAC address.

[Eric]

You can change your router password or block the other person with router password lock. In other setting you can go in networking sharing option and see the person IP who using your internet services, so you can block their system IP too.

[tumbleweed_biff]

Turn on MAC address filter and either set up a black list where you specify the computers which are blocked or create a white list where you list all the devices authorized to connect. The latter is more secure while the black list is much easier to set up.