Hello Scott,
forum profile is linked to the account created on our webpage. You can change the nickname that will be shown on the forum in your account details (https://www.capturingreality.com/my.account).
Regarding changing the avatar, unfortunately, it is not possible to change it here but you can find the tip here:
https://support.capturingreality.com/hc/en-us/community/posts/115002199052/comments/115000803511