change_acf_meta_keys

function change_acf_meta_keys() {

	global $wpdb;

	$values = array(
		"0" => array(
			'old_value' => 'foo1',
			'new_value' => 'bar1',
		),
		"1" => array(
			'old_value' => '_foo1',
			'new_value' => '_bar1',
		),
		"2" => array(
			'old_value' => 'foo2',
			'new_value' => 'bar2',
		),
		"3" => array(
			'old_value' => '_foo2',
			'new_value' => '_bar2',
		)
	);

	foreach ($values as $value) {
		$old_value = $value['old_value'];
		$new_value = $value['new_value'];

		$querystr = "
		SELECT $wpdb->postmeta.* 
		FROM $wpdb->postmeta
		WHERE $wpdb->postmeta.meta_key REGEXP '$old_value'";

		$wpdb->show_errors();

		$metas = $wpdb->get_results($querystr, OBJECT);

		foreach ($metas as $meta) {

			$key = $meta->meta_key;
			$key = str_replace($old_value, $new_value, $key);

			$wpdb->query( 
				$wpdb->prepare(
					"
					UPDATE $wpdb->postmeta
					SET meta_key = %s
					WHERE meta_id = %d
					", $key, $meta->meta_id
				)
			);
		}
	}
}