Leanpub books and courses can have online forums available for readers to read and write posts on relevant topics.
Here are some instructions about how to change your avatar:
Sign out using the menu in Discourse in the top right (the circle face menu).
You will get signed out of Leanpub as well. If not, then sign out.
Sign back in and upload a new image on Leanpub at https://leanpub.com/user_dashboard/settings
Navigate back to the Discourse forums and it will work.
If that doesn't work for some reason, if you post about it not working on the forum here:
...then you may find that someone in our author community has an answer.
(If you want to know how to update your avatar/picture on Leanpub, please go to your Leanpub profile page here: https://leanpub.com/user_dashboard/settings.)