[aop]

I just upgraded from 4.0.9 to 4.4.4 and also bought a new template.
In my old template I used only thumbnail and detailed images.
Now, the new template, use thumbnail (150 pxl), detailed (800 pxl) and also product image (400 pxl)(product page).
Is there any way to get my detailed images and down size ( 800 to 400 pxl )them to accommodate my new product images, without have to do it one by one on a Photoshop style software ?.
Appreciate any help in this matter.
Thanks !!