Are you talking about the "me!" section of your profile/your userpage?
On the new site a pencil icon should appear when you hover your mouse over the "me!" section. Click on that and you can edit it. On the old site there is a small edit button at the top right corner. Clicking on that should be pretty self-explanatory.
It looks like you already have some text in that section of your profile though (which means you edited it at some point in the past), so if you're referring to something else, please be a little bit more specific if possible.