How to Resize Image in popup images(click to enlarge)

Hi..I want to my popup images not as big as i upload when entering new product. how to resize the pop-up images so when the images pops not as big as the original images??

Have you considered resizing the images on your local machine before uploading?

Might be a better idea. I always resize my images to what I want them to be before uploading. Optimizes the images for faster download.

let's take example : i've been uploaded image with size 800x600, and in my shop the image is show 400x350, so when i click the enlarge button the images show the real size(in this case is 800x600).

what i'm ask is how about when i click to enlarge, the images not show as 800x600 but 640x400, the reason i want that coz the images too large for the page so i want to resize it, so the pages not fully covered with the (enlarge)images.
How to do that?

The best way is as bobdog says, to resize the actual image files in Photoshop or whatever you use, and reload them.

Anything else will probably require editing javascript code.