Larger images not getting larger

[numberger]

Once again, I have searched the forums before posting but I am extremely unfamiliar with Zen-Cart and have to pick up work where another person left off.
My problem is that the images do not actually get larger, they get a few pixles smaller. I found the location to change the size of the large image popup window, but this did not help it just opens then shrinks back down to the small size. Basically I don't know where the code is to change it. Thanks in advance, post some questions if you need any more info!

[afo]

A link to the site would be invaluable for anyone trying to help you.