So you want to change your Avatar in WordPress. Luckily, this is easier than you may of ever of imagined. There is a great service called Gravatar.
Here is what you do.
1. Create an account at Gravatar. When you sign up use the same email you used on your account on your WordPress site.
2. Confirm your email and set your avatar.
3. On your WordPress dashboard, navigate to Settings > Discussion.
4. Set Gravatar for your avatar.