Header question

Hello all. I’m trying to replace my current header with an image that I have made. I’m currently using the ‘black-n-white’ theme.

I understand that I have to replace the header.png contained within the images folders in the ‘black n white’ theme. However, there is no such file.

I for some reason thought that maybe replacing the header.png file within the ‘default’ theme would have an effect on the ‘black n white’ theme, but it didn’t.

I’m absolutely sorry for my complete newbiness, but any help that you can provide would be greatly appreciated.

Thanks!