moses-aquarius

I dont understand the upload part, i got a web domain, that linked to an online word press editor, this is where im editing, have taken the code and copied into wordpad (so as not to lose anything)

I assume this is what i have to change

#root{
width:780px;
margin:0 auto;
border-top:0;
border-bottom:0;
background:url(images/body-back.jpg) 0 32px no-repeat;

but my problem is, say i have an image on my desktop, how do i replace the florista image with that, say my image is background.jpg, what would i type to replace, you say upload the image to the same place, but im not sure what that means (upload it to the internet where the floristica image is, how, the only time i’ve ever uploaded an image is on facebook)
I really am novice with this code thing, but i can figure all the colors out, i just want these damn flowers out of my life. haha.

I open style.css in the theme editor section of word press?
thats what i’ve done, this is where the heap of code is throwing me off.

I think this is the image url

http://tawdryproductions.com/main/wp-content/themes/floristica/images/body-back.jpg

So i look for this on the style.css sheet?
If i had an image on my desktop, how would i route that in its place.