Am I to assume you live with your brother and have a small home network?
If so, you have physical access to his PC that he accesses the router from?
Just get into his PC and he probably has the router address in his browser with the password saved.
Login to the router and change the password on him.
Of course, he is your older brother, so you will probably get beat. But atleast you can surf the web while he is hitting you...