How do I add a custom image to the header of my blog?

Editing How do I add a custom image to the header of my blog?
Not all of the themes provided by UMW Blogs allow you to add a custom header image. In fact, each theme has its own options through which you can customize the look and feel of your blog, so the theme in effect is much more than just look and feel -it is also functionality and possibility.

Below is a list of themes we currently support that allow for a customized header image:
 * Ambiru
 * Anubis
 * Blix
 * Contempt
 * Cutline
 * Fauna Beta 2
 * Fjords
 * Flex
 * Freshy 1.0
 * K2 0.9.1
 * LetoPrime 0.9.6
 * MistyLook 3.3.1
 * Ocean
 * PressRow
 * Regulus 2.2
 * Rubric
 * Semiologic 4.3.2
 * Striped Plus 1.0
 * Steam 1.0
 * Sumenep
 * Tarski 1.5
 * Wordpress Default 1.6