Remove space around header image

I am using a child theme of TwentyTwelve and I would like to completely remove the white space above and on the left and right of my header image so it spans the whole way and connects with my background image.

I have tried a heap of other solutions that I have found on this forum but none have worked. I’m quite new to WP and editing style sheets etc.

My blog is – https://www.stampinstuff.com.au/blog/

[No bumping, thank you.]