Image Sizes Can't find main image div

Hi, When I go to files I see an image size for thumbnails, and an image size for the pop up. There are two blank image fields. Image Width and Image Height. First is that for an image on the product page or is that just for an image size if you don't use the thumbnails? If it is not for the image on the product page, I have been reading the forum, and I know I have to find the div for the main image, change the height and width, and then delete the thumbnails in the media/hikashop_com/thumbnails and then recreate them, at least that what it seems. Where is the div id main image file so I can change it. I just need to know where that is.

Thanks,

Jay