How can I extend the wifi to my room?

[Shorty]

So i rent a room with my boyfriend and the people we live with have wifi. The problem is the kid always changes the password and when we ask for it, he gives it to us but changes it again without telling us the new password. What a douche. We so pay for the internet as well. Anyways, my question is, is there anyway I can get ny own wifi router/modem whatever it's called and somehow connect it to theirs without him knowing? If so would I still need a password everytime he changes it or will it automatically do it itself?