XBOX 360 Removal of Family Settings
I bought a second hand XBOX 360 4GB Slim in black with built-in Wi-Fi. To my chagrin, and no little annoyance, I discovered when I tried to play Call of Duty 4: Modern Warfare that I was prohibited due to parental control settings. I did momentarily think of returning the machine to the store, but since that was 90 miles away I looked for an alternative solution online.
There are in fact more solutions online than you can shake the proverbial stick at. All but 1, after three hours trial and error failed. Reproduced below is the one combination that actually worked on my machine:
Dashboard->Console Settings->System Info
Left Trigger,Right Trigger,X,Y,Left Bumper,Right Bumper,Left (D Pad),Right (D Pad),Left (D Pad),A
You will then receive a dialog confirmation box. I found that it purged my network config and monitor setup, but retained my XBOX Live! profile.
Hope it works for you, but I suspect whether it does or not is contingent upon your precise model and age.