Removing theme borders and more

Hello. I tried to make a header image with a transparent background, but I don’t have the tools to do that. So instead, I made an image with the header on top of the background. But my problem now are the borders around the image.

How can I remove the border around the header? I am using Comic Press boxed with a child theme I am slowly customizing.

http://www.thedaemoschronicles.com/

If someone can point me in the right direction to make a background completely transparent, that would be helpful too.