Did anyone ever answer this for you? If not, you just click on your "Profile" tab right above the blog, and then click on the "Edit" button on the far right of the profile window. At that point, you should see a button over your "primary picture" to browse for a new one to replace it.
Upload your replacement pic, click the "Save" button at the top right of the profile window, and you're done.
Upload your replacement pic, click the "Save" button at the top right of the profile window, and you're done.