Talk Blogging

I have installed Wordpress for my blog from CPanel (wordpress version 2.0.4.). The problem is that I cannot change the header image from the default theme (kubrik) . Even though I've replaced the file kubrikheader.jpg on the content folder with my customised one, on my blog it's still the same default blue image. I must mention that I've done the same thing on an older version of Wordpress and it worked fine. But on this version, 2.0.4. I can't change the header of my blog. What can I do to solve this problem? Thanks a lot !