Changing Twenty Eleven's Header dimensions

I’ve made some changes to my blog which uses a child of Twenty Eleven. I see where to change the width of the wrapper, but the Header tool still insists on making any header image conform to 940 x 198. Maybe there’s a script supervising this?

Is there a way I can change it to the pixel dimensions I need the header image to be?

Would also like to eliminate the space to the top of the header image and have it be flush with the top of the page.

thank you for any clues or information about this!

blogcat