Unable to change the priority with ‘remove_action’ and ‘add_action’ in child theme

Your child theme functions.php loads before the parent theme’s, so you’re trying to remove the action before it’s added by the parent theme.

Hook after_setup_theme to remove/add, which is executed after both child and parent load.

add_action( 'after_setup_theme', 'wpd_wp_head_function' );
function wpd_wp_head_function() {
    remove_action( 'wp_head', 'woothemes_wp_head', 10 );
    add_action( 'wp_head', 'woothemes_wp_head', 2 );
}