User avatars display on your account and when you post on different areas on the website.
If you have Gravatar linked to the email you used on your account that will show up as the avatar. You may have set this up when signing up for a Wordpress account or site.
Changing Your Avatar
Like many of the settings for your account you will need to hover over the "Account Name" at the top right hand corner of the website. Select "Account" from the drop down.
From the account page, you will want to click on the Avatars tab. This will take you to a page where you can upload your avatar.
Click on "Choose File" and locate the avatar image from your computer. It is best for the image be square (example 100x100, 320x320, etc.) and a png or jpg (jpeg) -- sorry no animated gifs. Then click on "Upload".
Your new avatar should now be displaying.
Managing Multiple Avatars
If you upload multiple avatars they will be stored on your list on the Avatar page. You can click on any of your avatars to swap them out.
If you would like to delete an avatar, you will just need to click the delete button underneath the avatar that you would like deleted.