Press the Open/Close button on your remote control to open the drive tray
Press the buttons 1, 1, 1 and then 1 on your remote control, in order, one at time
Press the button 01 on your remote control to select Region 1, or 02 to select Region 2, and so on, or enter 13 to select Region Free
The word Region and then the number you selected should briefly appear on screen to confirm that the hack has been successful
If you are unsuccesfull with the above code then it may be worth trying one of the resources below.