re size page image

Ok I am trying to increase the width of the page featured image but I just can not find the appropriate css or lines of code, can somebody please advise me

Below is a link to show whats happening and as you can see the image is not fitting to the screen width.

https://plus.google.com/104381011591650113156/posts/ZcMS1QQjwdV?pid=6179084506300908018&oid=104381011591650113156&authkey=CP2BqqDwu_SWGQ