I think you can only upload music into the Google cloud from your desktop using the Music Manager. There isn't any way of doing it directly from your phone at this time.
You can easily change album covers on Google Play Music on the web. Just go to your Albums, click on the little arrowhead that appears under the album cover when you hover the mouse there, select Edit Album Info, and click on the album cover to change it. You'll need to have the actual image file on your drive in order to upload it as the new album cover.