You don't need to edit any of the scripts files. All of the code to change validations is on the page.
It uses a combination of Spry and WebAssist Server Validation. If you own Dreamweaver you can update the spry validation using the DW properties inspector. If you own Validation Toolkit you can update the server validation using the server behaviors panel.
If you need to do it by hand all of the server validation code is on top of the page and can be commented out. All of the spry validation is on the bottom of the page and can also be commented out. The digit length of the validated field should be clearly visible as a "4" in both the spry and webassist server code associated with that form element. You should be able to simply update it to a "2".
