If will here explain how to change the default login url in WordPress from /wp-login.php to /login. You can change wp-login.php to anything you want.
Open your .htaccess file, and add this code before any WordPress rewrite rules,
This code will redirect any one visiting to http://yoursite.com/wp-login.php to http://yoursite.com/login, and you can then login at this new login url.