I wasn't sure how to do this either, but had a click round, and if you go to your profile on the main part of FD, not the forums profile, and change from FitDay 2.0 to Fitday Classic, it will then give you the option when you refresh to FD Classic to go to a public settings page for your Fitness Jounal and make it public. Hope that's clear enough. I don't know if anyone else knows an easier way to do it though, that was quite long winded.
Start: 137.0 (14/09/2012)
Current: 131.6 (19/10/2012)