Family Password

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

As long as your talking about the Xbox 360 and as long as you are able to download your profile to the console they have actually set it up so you can reset it yourself the steps are in the following link.

https://support.xbox.com/en-US/xbox-360/security/forgotten-parental-controls-pass-code

Otherwise like M3tal Daz3 said you would have to contact xbox support.

Make sure that you have an adult Microsoft Account, then go to https://account.microsoft.com/devices and sign in with your adult Microsoft Account.

Register the console's serial number to your account if not already done so.

After you registered the console, and it shows on the list of devices, click on "More Actions" and then "Reset Passcode" to reset the passcode for that console.

For this issue you would need to contact xbox support:
http://support.xbox.com/contact-us

Hi Marcobr18,

Thanks for contacting us. In this case, I'd reset Xbox to factory defaults, find out how here: https://support.xbox.com/en-US/xbox-one/console/reset-console-to-factory-defaultsHope
this helps!