I found this after poking around for a while - go to your Sparkpage and click on See All Awards (on the left side of your page)
This will open up a page that shows all your goodies, Streaks and Trophies
At the bottom of the Trophies it will say Manage My Trophies - click on that
The page that opens shows all the trophies you have but at the top where the picture of the guy is, there's a little grey box that says
Add Weight Loss and Sparkversary trophies
This will open up a page of trophies that you can choose from - click on the ones you want!
| current weight: 233.2