Can someone help me figure this out?

I'm trying to change my weight in the charts area. I want to be able to get the most out of this app but this has been, by far, the most difficult to figure out! Lol. I have been tapping and holding everywhere on the chart/graph and nothing. I've done most of my personal info in the 'Me' section but why is it I can't change the chart? Is there something I'm missing???