if i understand you correctly, you go to the coverarts section, and when you click on an alubm, and then it zooms in, you click the defualt image again and the thing slide to the right, and on the left, displays the cover art?

if that is true, you just need to select the image you want to use by clicking on the smaller image on the left.
it will make the larger image the same, and then just tap on the larger image again to get itto slide back to the left