If you have to or want to change the domain of your WordPress MU site. The domain name is actually stored in different places in the database, as well as online in wp-config.php. Every instance of these will need to be changed.
Before you do anything create a backup. Go to phpMyAdmin, select your database, and choose Export. Save it to your computer. We’ll be making a copy of this and working on the copy. This way, if anything goes wrong, we still have our backup.