Change Image Size On Product Description Page

The size of the image for the categories, category, and the pop-up image is fine, but I can't seem to find where to set the size for the product description page. The image for that page is resized to 120x91 and is too small. Where can I change that please?

Thanks!!

You can change that with the "thumbnails height/width" options of the Files tab of the configuration.
Note that each one of your menus and modules has its own height/width options and if you don't set them, it will use these same options. So you should go in your menu Display->Content menus/modules, edit each one of them and set the image height/width options to the size you want for your listings.