Parental Control on. Bought second hand so don't know passcode or security question to change ...

You would need to contact support and they can help you reset it. 1-800-4my-xbox if you're in the US/Canada or http://support.xbox.com/contact-us

Hi there,

From the console, go to Settings > family > select a content control setting > when prompted, enter the passcode.

If you don't recall the passcode, you can select Reset Pass Code and answer the pass code question that appears > select Done.

If you don't know the answer to the passcode question, you'll have to contact Xbox Support so they can assist in resetting it:

support.xbox.com/contact-us

More details can be found here:
support.gtm.xbox.com/.../xbox-live-parental-control

I hope this helps.

That depends, are you referring to the Xbox LIVE passcode (to sign in to the account) or the Parental Passcode (download content, change settings)? The LIVE passcode can simply be reset by recovering your account, or going into the menu and disabling it
(requires the passcode). The Parental passcode will not be affected by recovering, and can only be disabled by knowing the code or answering the security question.

Prince: This is incorrect. Recovering an account will only reset an Xbox LIVE passcode, not the parental passcode.

Dodge: The only way you can remove a parental passcode is to A) know the passcode, or B) know the answer to the security question.

The only way to edit or remove the Parental Setting passcode is to A) know the passcode, B) know the security question, or C) call phone support, prove ownership of the parent account, and get a reset code.