How To Modify the Guest Welcome Message
You can modify the guest welcome message that appears on the forumhome (index.php) to unregistered users by modifying the first_visit_message phrase.
Admin Control Panel >
Languages and Phrases >
Search in Phrases >
Phrase Variable Name Only: first_visit_message. From the result click on the
[edit] button and in the English text field click on the button
[Copy Default].
Now you can modify it and change it to whatever you want. When done, you click on the
[Save] button.
(Initially you find it by going to Search in Phrases and at the 'Search for Text' field you type in: 'If this is your first visit' and click on the [Search] button)