If you want to modify copy/text on this page, it’s very simple. Just go to YOUR-TEMPLATE directory under language dir to modify the way you want.

includes/languages/english/html_includes/YOUR_TEMPLATE/define_contact_us.php

However, if you plan to modify the form significantly, you’d look to spend more time to add codes in order to process the form. There’ll be multiple files you’ll have to open to modify in a PHP Editor such as EClipse or NuSphere client software. You can also add more php files and use require_once function to includes those files in your codes.

Number of files below will be involved during the changes:
– includes/languages/english/html_includes/YOUR_TEMPLATE/define_contact_us.php
– languages/english/contact_us.php : define all new constants in this file to be used in Contact Us form
– includes/modules/pages/contact_us/header_php.php : you can modify/add new logic in this file to collect user’s inputs from the form. You can add more functions to this file such as sending notification to more than 1 support admin, or filter inappropriate data from user’s inputs…