The header images are stored in your themes directory. For example you want to change the header image of default theme by wordpress. Then go to wp-content/themes/default directory.. Go to Image folder and you will find the header images there.. Just change this image using http://FTP..
Also, you could go to to the themes directory and search for a theme that allows your to upload a header through the WP admin. A search like this will bring back several.
http://wordpress.org/extend/themes/search.php?q=custom-header
just upload a new image in ur wp-content>>themes>>your theme>>images directory.
Now look in the header components section in ur style.css file for the image link and change the image file name to ur newely added image filename.
hey thanks for your answer… I dont have image link because I did my theme from scratch! I am able to put a image as background but as I want a link on it, it cannot be background.
is it a issue if the image I am trying to put is outside my theme folder?
look for this piece of code in your header.php file.
<h1>
<a href="<?php echo get_option('home'); ?>/"><?php bloginfo('name'); ?></a>
</h1>
<div class="description"><?php bloginfo('description'); ?></div>
replace it with :
<h1>
<a href="<?php echo get_option('home'); ?>/"><img src="http://yourwebsite.com/theme/image.png"></a>
</h1>
<div class="description"><?php bloginfo('description'); ?></div>
so that your blog title is replaced by an image and it will still link back to your home page.