Change background colour/width/image etc.

You need to edit your theme’s stylesheet – usually called style.css.

CSS Tutorials
Learning CSS

Thanks for your reply,
I have looked at the style.css on the WordPress editor! But I still dont know what to change I have edited these properties, with no visible effect (it seems):

body {
font-size: 62.5%; /* Resets 1em to 10px */
font-family: ‘Lucida Grande’, Verdana, Arial, Sans-Serif;
background: #000 ;
color: #000;
text-align: center;
}

#page {
background-color: black;
border: 0px solid #959596;
text-align: left;
}

I was trying to change the background colour here but nothing seemed to change at all! Was wondering if you could tell me what the code for Background colour, Page width would look like and how to change the header image? Can i just link it to an image in my website folder?

Also, would I be able to save the page on my computer, edit the code in dreamweaver (this would be easier for me). And then copy the code into the appearance edit function?

Can i just link it to an image in my website folder?

yes, you can link to an image in your website folder, best using absolute file path.
often the images for custom headers are saved in the images folder of the theme.
wordpress helps you with the ‘bloginfo()’ tag to get the absolute path right regardless on which page your are:
src="<?php bloginfo('template_url'); ?>/images/custom-header.jpg"

referring to your last question – you could download the style.css, edit it locally with dreamweaver, and the ftp it back up.

to see changes you made in the styles, you may need to refresh the browser chache by pressing CTRL F5 at the same time.