FTP to /var/tuxbox/config/enigma and find a file called 'config'.
Right click it and select 'view'.
Look for a line like...
Open up your windows calculator and go to scientific mode.
Click on the HEX button.
Enter in the last 4 characters in the parental lock line in the config file.
Click the DEC button.
This is your 4 digit pin code. You can then use it to disable the parental lock or Setup lock on your image.
If you can't ftp, your only option left is if you have the tuxbox commander plugin installed in your image, in the plugins menu (Blue or yellow button). You can navigate to the config file using this plugin and edit the file here.