I believe that you will need to call DirecTV as the BEST option....
The Parental Control passcode can be reset remotely by DirecTV customer support.
However, there are a few caveats.
Your receiver must be connected to the phone line in order for DirecTV to gain access and reset the passcode.
You must be able to prove that you are the owner of the DirecTV account.
It can take anywhere from 30 minutes to several hours to take affect.
Call the DirecTV customer support line. Tell them that you have forgotten your parental control passcode and request to have it reset. Expect the customer support representative to ask for the last 4 numbers of your social security number and/or credit card number. They will not, under any circumstances, reset the code if you can't prove that you are the account holder.
The following should only be a last resort option that involves completely resetting your receiver back to system defaults.
In your menu, under "System Settings" select "Reset", and then select "Reset Everything". That will solve your problem, as it will erase all previous settings and you will go through the set up process again.
WARNING: This will erase EVERYTHING on your receiver. All of your recorded shows, settings, favorites, and programs set to record will be gone.
This should only be done as a last resort option.