Once you are logged in, you are presented with the screen above. It's rather sparse. You can add images by uploading them. You can delete pictures you don't like by clicking the corresponding X below the picture you wish deleted. And you can select the current picture you want to be your Gravatar, which will then have a blue border around it.
If you have an old picture you now despise, go ahead and upload a new one and delete the old one. It happens to everyone.
