header featured image full width

hello, i'm tryng to set the header featued images for single pages (every page has is image) full witdh like the slider images for home page, but I don't know how to do that, the images have a margin on top, left and right; the site is not online yet, so i put the screenshoot there: http://www.isabilla.it/imgs/ERR-BORD.jpg thank you! Isabella