How to replace the default search menu in Buddypress

I have buyed this plugin from codecanyon: http://codecanyon.net/item/wordpress-ajax-autosuggest/4248819?sso?WT.ac=search_item&WT.seg_1=search_item&WT.z_author=codenegar

I talk to the owner of the plugin, and he said, I should put this code in my theme: <?php ajax_autosuggest_form(); ?>

I should first enable the ajax autosuggest widget in the auto suggest placeholder. I have done that. But the code, I dont know where to place it. I have some php folders that is name search.php and searchform.php. Should it be in there og be in the header?

Do anyone of you know how to disable the default search, so I can use this, I have bought?