On your remote control, press the
home/TiVo button on the top right to visit the Home Screen.

Using the arrow keys on your remote, select Menu.

Navigate down and select Parental and Purchase Controls.

Using the number pad on your remote, select a 4-digit PIN. This will be used for managing your Parental Controls and Purchases.

Once you've chosen your PIN. You can configure your Parental Control. 

When Parental Control is enabled, a lock icon will appear on the Home Screen next to the Menu icon.