Making thumbnails bigger

I’m tweaking etsy-shop.php, and trying to figure out how it works. First, I was able to get rid of table and replace with divs, but now I’m trying to get a different image size. I was able to load a bigger image (570xN), but the width and height attributes on the img are causing the image to be small. I can’t figure out how to omit those attributes. I can override them with my own attributes but that doesn’t help me; I just need to omit them so that the image that is loaded is not altered. Any help?

I know this will break with the next update.