Hi Bovic,
Here’s who to adjust the height of your hearder image in Twenty Ten:
(I’ve just done it for my own site: https://www.versa-teksten.nl I reduced it to 4px! So It’s the line above my menu now.)
Go to appearence/editor/theme functions (that is functions php).
About a quarter into that file you’ll read:
// Add a filter to twentyten_header_image_width and twentyten_header_image_height to change these values.
define( ‘HEADER_IMAGE_WIDTH’, apply_filters( ‘twentyten_header_image_width’, 940 ) );
define( ‘HEADER_IMAGE_HEIGHT’, apply_filters( ‘twentyten_header_image_height’, 198 ) );
If you change those numbers (940 for width and 198 for height) you can costumise your header image Mine is now 840×4. And this will change the numbers in the header upload page as well!
Good luck with it!
Karin