First make sure you're logged in. You should see "Welcome, {your user name}" in the right corner.

Next, click on the "Your Stuff" dropdown menu in the top navigation.

Select "Profile"

Click the "Edit Profile" link that is next to your avatar photo.

Scroll down to your avatar and click the "Change" link under your avatar.

Click the "Save Settings" button.

This next page is where you can upload a profile photo from your computer, crop, review and save.