1. On the top of your screen, you will see many options such as Notifications, Settings, My Profile... Click on settings.
2. Then on the left side of the screen, you will see many boxes such as My Subscriptions, My Messages, My Settings... Look under the My Settings Box.
3. Under the My Settings Tab, you will see "Edit Avatar." Click on that.
4. Choose an avatar which you like whether it be a custom one or one you find on google (has to be 100x100 or lower).
Save changes. Inshallah you will benefit from this forum and enjoy the threads found here as well. If you have any questions, ask in the appropriate section.