First make a backup copy.
Then open it up in Wordpad (Not Word!)
Find the line #header
Replace ‘images/kubrickheader.jpg’) with the name of your image eg ‘ploop.jpg’
Save the file & upload it to your server, overwriting the original.
Make sure your ‘ploop.jpg’ is in the http://plooptionary.com/wp-content/themes/default/images directory.

And that should do it. Of course there are more elegant ways, and you can have the image in a different directory if you edit the file path, but this should work.

I’d recommend getting a new theme anyway, as Kubrick is over-used-Choose one with an image in the header already, and it’s a simple substitution job to get in place.

BTW, an even faster way to change the image is to rename your custom image ‘kubrickheader.jpg’) ‘ and overwrite the original, but that’s cheating