You can change your profile picture (avatar) by doing the following:
- Tap on the profile icon at the bottom right of the screen to open your profile screen
- Tap on the 3 dots at the top right of the screen
- Tap "Edit Profile"
- Tap on your avatar image
- Tap "Choose photo" to choose an image from your camera roll, or "Take Photo" to make a new one.
- Tap "Save"
- Tap the Back Arrow and you're done