Hi Benita,
When uploading your photo onto Image Shack there is a 'drop down' menu which gives you the option to choose a size relevant to where you are going to post the photo.
i.e: 320x240 for websites and emails
640x480 for message boards.
So if you know that you have selected the 640 option you can go back and re-do it to the 320x240.
Eileenxxx