How to change a sites URL
This is basically a system admin question rather CiviCRM specific. I personally don't have very good experience in doing this but when there is URL changes


Make sure your new domain is pointing to correct server IP
Update the url in apache or nginx conf.
Update .htaccess file in your site directory if its using any base url.
Update the base url in wp-settings.php or drupal's settings.php file.
Update the base url in civicrm.settings.php file
Clear drupal and civicrm cache
If using wordpress you may need to update in database 


Query:

UPDATE wp_options SET option_value = 'http://new_domain.org' WHERE option_name IN ('siteurl', 'home');


Cheers

Pradeep