The key with customizing WordPress is learning which files control what area. I spent my first 2-3 weeks really familiarizing myself with all the template files. I'm not a skilled programmer and just know the basics of CSS so at first it was a bit of a challenge.
But I just started breaking it down piece by piece. For example if you see want to change something at the top of your blog, open the header file. If it's a color, chances are it's on your style.css file. For your footer, open the footer.php file.
For images, what you can do is right click the image and view the properties. This will give you the path to the image. For example, this is the path to my blog's main logo
http://blog.2createawebsite.com/wp-c...mages/logo.png
So I know if I want to replace that image I need to upload my new file to that same location with the same name to overwrite that logo.
Try finding a template that doesn't have a lot of images and just customize the logo by overwriting the existing one....
http://themes.wordpress.net/
What exactly is giving you problems? Is it changing an existing image or are you trying to change the size of large areas, etc?