Darn gotta figure out how to post in the forum so it doesn't apply the code and just shows it. Back in a moment to repost. Still can't get the code to show so I placed in in a pastebin post for you..
You have already been given more than enough help to fix this issue. But since it seems you aren't paying attention to those helping you here is a quick fix.
In header.php of your theme you see the below lines of code:
<h1>"><?php bloginfo('name'); ?></h1>
<?php wp_list_pages('depth=1&title_li=' ); ?>
This part <?php wp_list_pages('depth=1&title_li=' ); ?> right there is what is making the page title links show up in the right hand side of the top of your site.
"About" is one of the pages you have in your site. Simply changing the link name will only change the text shown for the link. It will still link to the page created in wordpress that was originally named "About"
The only way I can think of to remove the wordpress page listings in that spot and add only a link to your forum would be to change the code bit in header.php
You could remove the <?php wp_list_pages('depth=1&title_li=' ); ?> part all together which will remove the links to the wordpress pages in your site. Not sure if that is what you want to do or not but any how read on..
So if you were to say replace the above section of code I showed you at the top of this reply with the code in this link http://wordpress.pastebin.ca/294215 then it will get rid of all your wordpress page links in that section and give you only the link to your forum.
If you do remove the <?php wp_list_pages('depth=1&title_li=' ); ?> tag from the header as shown above I would think about putting it in the sidebar maybe. That way your visitors will still be able to find your wordpress pages.