If you used a domain "olddomain.com" and want to change everything to a new domain "newdomain.com",
there is an easy way to tell search engines and redirect users to your new site.
Just add this to .htaccess file on "olddomain.com" site:
RewriteRule (.*) http://www.NEWDOMAIN.com/$1 [R=301,L]
and all urls of your old domain will redirect to the same URLs on a new domain with 301 code.
So if customer or search engine hits URL:
they will be automaticaly redirected to
and search engines will know that URL was permanently changed and will update their indexes faster.
Do not forget to setup a new SSL certificate for your new domain if you are using secure checkout there.
Old SSL certificate will not work with a different domain.
Let us know if you need help with any of this.