I can’t find the source code (html) file in my wordpress folder.

Help!

I need to change a line of code in the source code file for my blog.
I want to change the size of the pixel image kubrickheader.jpg
Here is the the code in firefox, but i need to edit it!
However I cannot find the file in my WordPress folder.

#header { margin: 0 !important; margin: 0 0 0 1px; padding: 1px; height: 198px; width: 758px; }
#headerimg { margin: 7px 9px 0; height: 192px; width: 740px; }

mvh
Chris Adam
[email protected]