installing header image

You don’t add a header via the Presentation tabs in your admin. That is where you change the Styles. You can use the Theme Editor under Presentation to open your style.css or header.php template files and change the header information there.

If you are using Kubrick (WordPress default theme), there is a tool that will change the header easily for you at http://www.redalt.com/tools/kubrickr.php.

Other options would be searching…
Or see at the Blog_Design_and_Layout in Codex.