Should you wish to change your website domain name from an existing Metro Publisher instance you must follow the basic instructions here: Taking Your Website Live.
To make sure there are no broken links you should make the new domain the primary one.
You should also leave the old domains in place so that anyone using an old bookmark will be redirected properly.
Please also make sure you update your Google Search Console: Moving Your Website.
If you also have your site registered with Bing (recommended), you should move the domain name there as well: Bing Site Move Tool.
Thanks to automated 301 redirects, the impact on your existing Search Rankings (SEO) will be minimal if you follow these instruction.