Placing header image on top

Hello,

I am using Megaresponsive Lite theme and I almost finished customizing it to my needs, just don’t know how can I place the header image on top of the page similar like in this example link

My site address is here: https://goo.gl/wMAjBa

I know I would need to use two images, because the site changes its look according to screen size, but don’t know what’s the best approach to do it.