How do i disonnecr from xbox live with an xbox 360 slim?

I want to do a glitch in Castle Crashers but i have to be disconnected from xbox live for it to work. On my old xbox, i was able to just unplug tht white little box thing in the back of the xbox. Thats not there anymore. I dont hav an ethernet cable and my dad is always on the computer becuz he works from home so i cant unplug the router