If you forgot the parental's lock password from your PlayStation 2 or if you want to remove the Parental Level completely check this quide.
To change the password:
1) Wait for password screen to appear where you have to actually enter the 4 Digit pin code.
2) Hold Select whilst enterting the code '7444'
3) It should say something like Password Deleted, then ask you to register a 'New Password' obviously type something in you'll remember this time!
If you want to remove the Parental Level completely try the following :
1) Insert a DVD movie and start the actual main movie off playing
2) Press 'Select' button to bring up DVD naviagation control and then select 'Title Menu'
3) Press 'R2' Twice - you should get a 'The Operation You have chosen can not be performed' message
4) Press 'Select' button again
5) Navigate to the 'Setup' icon and select it
6) Now you have 4 more Options : 'Language Setup', 'Screen Setup', 'Custom Setup', 'AudioSetup.
7) Select 'Custom Setup' followed by 'Parental Control'.
8) You will be asked for your 'Parental Password' type it in and you'll get some more options that were previously locked.
9) Select 'Level' and select 'Off' to avoid ever seeing that annoying 'Parental Control' screen again!!