This has been answered many times. Search this site, as toscho points out above.
And see Ben Word – Hide WordPress, who shows how to:
1 – Clean up the output of wp_head and removing the generator from
RSS feeds2 – Hide /wp-content/ by rewriting static theme assets (CSS, JS, and
images), rewriting the plugins directory, and also changing the
location of WordPress uploads3 – Clean up the output of navigation menus with a custom walker
4 – Show root relative URLs