How do I disable parental controls?

No. There is no way to circumvent the parental controls or restrictions passcode.

The only way to get rid of it is to restore the device to factory settings using a computer (does not need to be the sycning coputer). If the Restrictions passcode was set and a backup performed after, the passcode will be in the backup and will be restored with the backup. So the only way to get rid of it is to restore to factory defaults and not restoring the backup.

Follow the instructions in iOS: How to back up your data and set up your device as a new device http://support.apple.com/kb/HT4137 to restore the device to factory settings.

Once you have setup the device as a new one, you can then sync it back with your iTunes account and all your music, apps, contacts and any other content sync'ed with iTunes will be loaded on the device. Any content that is stored only on the device and not sync'ed with iTunes, like app logins or data, will be lost during this process. Be forewarned that this is a long process and can take a couple of hours or more to complete. This can be painful, but it is necessarily so to prevent users from working around the security settings. After the restore is complete, you can setup a new Restrictions passcode. Make a note of the passcode to avoid this situation in future.

 Cheers, Tom 😉