For changing you site URL and domain name to new one you can do it by editing your database using phpMyAdmin or by editing wp-config.php file.

Method 1 Change domain name using phpMyAdmin

First go into phpMyAdmin, select your WordPress database from left column then find a table name wp_options, bear it in mind that in your case prefix wp_ could be different. See below image.

See above image carefully. Now edit both siteurl and home address to your new URL and domain.

Method 2 Change by editing wp-config.php

Open your wp-config.php file in text editor then add below code just above this line /* That’s all, stop editing! Happy publishing. */

define('WP_SITEURL',' ');

After adding above code save your wp-config.php file and upload it to your server. After login to your Admin panel don’t foget to change your domain name from Setting>General

WordPress Address (URL):
Site Address (URL):