I'm a newbie ... sorta
Go to the top of your page and press: My Account
Then select the tab that says: Health Tracker
Then on the right side, click: Go to Health Tracker
Then you can type in your Current Weight.
If you want to check it, go to the Ticker & Widget tab and you can see if the change is reflected on your ticker.
It may take a few minutes before it shows up on posts, but it should be changed.
I hope this helps, I'm not very computer savvy, but this gets me to it. lol