I would like to widen Fresh and Clean theme so that the content area fits 640 images. Also, is it possible to remove the lightening of photos when hovering and remove the border around photos when a caption is added?
Since the theme is responsive, it would be good to stick to percentages for width. This example will make the main content area in the Fresh & Clean theme about 640 pixels wide:
This example affects the home page as well as posts.
You should also adjust the content width setting on the Appearance → Custom Design → CSS page to match.
If you have inserted images from outside sources at a fixed width, note that they won’t adjust automatically and you may need to remove and re-insert some of the images if you want them to be full width.