I'm sorry I wasn't clear enough.

I created the watermarks myself so I probably shouldn't have mentioned that, as I forgot that IH4 can generate watermarks. I can see where that might have caused confusion.

I simply want to make new images and have them replace the images I have now, and (hopefully) have IH4 generate the sizes I need.

So to do this I would need to save the new images with the exact original name I used, upload them to my image folder via FTP, and then go into the zen cart IH4 admin to clear the cache and it should generate the resized images like it did originally? I sure hope I don't need to go in and update every single product individually as I have almost 1000 that I would have to sort through. :-(

Thanks, by the way, for your responses... it's appreciated!