On The Web:
To add a profile picture to your account, click your name in the top right corner and select Account.
Scroll down until you see Avatar. Click the Choose File button and upload your picture.
Hit Save Information at the bottom of the page to save your selection.
On The App:
Click the Account tab in the bottom left corner of your app. You'll see a spot for Profile Photo on your account page. You can either take a selfie with your phone or choose a photo from your library.
Click Confirm, once you have the correct photo selected and you're good to go!