Thankyou for that. Would i just use the code as you have types it, or would i need to edit to $new_title?
$post->post_title = get_field('site_name', $post_id).' '.get_field('site_location', $post_id);
if ( get_post_type( $post_id ) == 'sites' ) {
<ul>
$new_title = get_field( 'site_name', $post_id );</ul>
$new_slug = sanitize_title( $new_title );
}