function my_custom_login_logo() {
    echo '<style type="text/css">
        h1 a { background-image:url('.get_bloginfo('template_url').'/images/login-logo.png) !important; }
    </style>';
}

add_action('login_head', 'my_custom_login_logo');

Add the following line to code to your theme's functions.php file

Change Wordpress Admin Logo

wordpress

PHP