You can update your header photo from this place, too. Just click the silhouette and head to 'Profile' and then click 'Edit Profile' on the right underneath the blue bar. The default picture is a silhouette, but you can make your avatar whatever you want (your face, a dog on a skateboard, the possibilities are endless). Choose something you like that you think isn't taken, but also something easy to remember for others. That will be your username, or handle, and people can notify you by typing in front of your username in a tweet. Step 5: Once you're in, click on the grey silhouette next to the 'Tweet' button on the top right of your screen, and click 'Settings & Privacy.' At the top, you can pick a username you like.