Changing the WordPress Address (URL)

Please could someone help me, I have installed wordpress on my synology nas and are not able to change the WordPress Address (URL) field under general settings, the field is greyed out. This results in I’m not able to access the wordpress admin site from my domain url. I can access the workpress external but only text. I have also tried the suggested solution but without any luck.
• I have tried to update the wp-config.php with
define(‘WP_HOME’,’http://example.com/wordpress’);
define(‘WP_SITEURL’,’http://example.com/wordpress’);
• I have also tried to edit both the siteurl and home field directly in the wordPress db..
• I have also disabled all plugins.
However, in the settings tab of wordpress the field is still grayed out with the localhost 192.168.1.XXX/wordpress rather than my domain.com/workpress url.
Do anyone have an idea? It would be greatly appreciated 