What is the code to set the path to a header jpg?

I’m trying to create a custom image header. It works locally but when I try it on a website I’m getting an error when I upload the jpg because the path is not found. I have this:

if ( function_exists(‘add_custom_image_header’) )
{ add_custom_image_header(‘header_style’, ‘admin_header_style’); }

define(‘header_width’, 576);
define(‘header_height’, 131);

if ( function_exists(‘add_custom_image_header’) ) {
add_custom_image_header(‘header_style’,’admin_header_style’);
}

What line of code do I need to set the path properly?

Thanks
Charles