Changing Parameters for the Payment Gateway - Direc Pay

We have a website that is up and running and has a payment gateway through Direc Pay - [login to view URL] The online gateway was working very properly until a few days back when the Direc Pay guys changed the parameters for accepting the payments from our website to their payment server, leading to our online payment processing being stopped. Need - a php developer - who can find the required files which stores the string that gets passed to Direc Pay - modify the string to the new required values as directed by Direc Pay - test the payment module using the DIrec Pay Test Servers - Change the settings to make it live once testing finished successfully. We are using the following - Zencart - PHP - my SQL (open)