Header background picture

Hi can somebody please help me add a background picture to my heading. I struggle to remover the one that came with the template, and now can’t add my own! :/
http://www.jennythehead.blogspot.ca

and the pic I am trying to add is here: file:///Users/mariatorres/Desktop/index.html

this is what it looks like now:

ont-weight: 500;
line-height: 15px;
}

.main-header {
width: 100%;
text-align: center;
color: #fff;
margin: 0 auto;
min-height: 290px;
clear: both;
/* background: #fff; */
padding-bottom: 20px;
padding-top: 20px;
position: relative;
background-image:
margin-bottom: 0;
background-repeat: no-repeat;
background-size: cover;
background-position: 0 100%;
background-attachment: fixed;
background-color: #444;