Go to health tracker and change your weight in your profile. It will then automatically change the weight on your ticker, if you've created one. However, it takes a few hours before it becomes "permanent," so if you post or reply to someone else's message shortly after changing the weight in your health tracker, the new weight won't show up.
age: 53 5'1" tall HW=231 SW=216 CW=139.8 GW=130