Redirection to Thank you page after Contact Form submission

First of all, 

Prepare a Joomla article that will be the "Thank you" page. 

We will redirect user to that page. Remember front-end link of that page.

Now, the hacking part. 

The file that you will be editing is /components/com_contact/controller.php. 

Lines 193-195 (in Joomla 1.5.15) should look like:

1.$msg = JText::_( 'Thank you for your e-mail');

2.$link = JRoute::_('index.php?option=com_contact&view=contact&id='.$contact->slug.'&catid='.$contact->catslug, false);

3.$this->setRedirect($link, $msg);

If you only want to change the text displayed when the contact form is submitted you edit the "Thank you for your e-mail" text below making sure to keep the single quote marks ' before and after.

If you want to make redirection to your "Thank you" page and disable information message, change this code to:

1.$link = JRoute::_('http://www.yoursite.com/thank-you-page-link');

2.$this->setRedirect($link);