You may delete your Avatar from the My Account page or from your My Forum Profile page.

If you use Gravatar your current Gravatar avatar will be used automatically after you delete a locally-updated avatar.

My Account

Scroll down until you see your Avatar. Click on the “Delete local avatar” button and click the “Update Avatar” button.

My Forum Profile

Select “Edit” from the menu on the left. Scroll down to the “About Yourself” section. Click on the “Delete local avatar” button and click the “Update Profile” button at the bottom of the page.