On the web:
- Visit your profile page, which you can access by clicking on "Profile" from the menu in the upper right-hand corner
- Hover over your photo, and you'll see an option to "Edit Photo"
On the mobile app:
- Visit your profile page, which you can access via the "You" tab
- Tap the "…" icon
- Tap on the option to "Edit Profile"
- From there, you should see an option to "Edit Photo"