Another WordPress Header Issue (awkward)

Right, I’ll do my best to explain this thoroughly enough.

I’m using the Elegant Grunge theme and I have opted for the extra sidebar.

e.g. like so: http://thetruejoe90.com/home

I’ve uploaded a transparent PNG file which you can see to the left of the header but I want to change the background of the header to this 1382px x 216px.

Looking through the style.css I have found (so i believe) the right section to make the alteration being here where it states double-right-sidebar:

#header-wrap {
	background: url(images/header-repeat.jpg) repeat-x center top;
}

#header {
	height: 216px;
	background: url(images/header.jpg) no-repeat center;
}

.no-sidebar div #header {
	background-image: url(images/header-no-sidebar.jpg);
}

.double-right-sidebar div #header {
	background-image: url(images/header-double-sidebar.jpg);
}
#header div {
	width: 800px;
	margin: 0 auto;
}

.double-right-sidebar #header div {
	width: 947px;
}

After uploading the file I still cannot get the desired JPG to alter the header.

Quite simply, I can’t see the wood for the trees! Assistance would be highly appreciated as i have spent nearly 5 hours trying to make this right but to no avail.