Cover image responsiveness

Hey Guys!

My problem is regarding my cover image. The responsiveness is completely off. I work with 3 screens, but the image is 3 different sizes on the screens. The only place the image responsiveness is correct is on my 13′ laptop. The image on the other 2 larger screen, is way to big. (Note that the text is written on the picture it selves)

How do i get the image to be responsiveness on all devices?

Thanks in advance!

The page I need help with: [log in to see the link]