Convert template from "rounded corners" to "square"

I've downloaded the following template开发者_JAVA技巧:

http://www.styleshout.com/templates/preview/Refresh11/index.html

But unfortunately, it has rounded corners and shades. I want it to have square corners and the shades should be removed, too. It should look like this:

But I'm not good enough at (X)HTML and CSS so I didn't manage to achieve this.

Could you please help me? How could I remove the rounded corners?

Please don't say "Take another template" ;) It's also for learning purposes :)

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The rounded corners and shadow here are accomplished by images, not code:

• http://www.styleshout.com/templates/preview/Refresh11/images/header.jpg
• http://www.styleshout.com/templates/preview/Refresh11/images/menu.jpg
• http://www.styleshout.com/templates/preview/Refresh11/images/content.jpg
• http://www.styleshout.com/templates/preview/Refresh11/images/footer.jpg

If you have control over the file system, you can simply edit these images to have square corners and no shadow.

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If its an image and you have access to it, as said above, you would simply put the image in photoshop,illustrator, or flash and alter to your liking. Taking out the shadows or making it look anyway you like. Assuming you are familiar with these programs.