To change your profile picture, go to the 'My Action' tab on your app and then click the settings symbol in the top right corner.
Once you're in settings, click 'Profile'. From there, you can change your name, username, or profile picture. To change your picture, just tap the camera icon. After that, you'll be able to choose a picture from your camera roll or take a new one. Click 'Save' once you're done.