Changing a tab URL

I did a search about this but all the results dealt with the Home tab and didn’t seem to address what I want to do.

I installed phpBB on my site. http://eaglerockcycling.com/home/ Then I created a page called “Forums” so I would have a tab called “Forums” with the other tabs. But that just takes me to a standard page within my blog that I had to add a link/url to so that you have a link to click to get to the forums. I would like to be able to just click on the Forums tab and have it go straight to the forum url. When I view the page source I can see that line 71 has the url for the Forum tab but I can’t figure out which .php page to go to to edit the line with the Forum’s url.