1. First, navigate to your profile page. You can do this by clicking your name in the top-right corner of the page and following the link in the drop-down menu.

2. When you're on your profile page, you'll see a box at the top with some of your most basic information, including your name and profile picture. In the top-right of that box, you'll see a yellow button marked "Edit." Click there.

3. A pop-up called "Edit Profile Details" should open. On the second row from the top, you'll see a box where you can add or edit your headline!