When you change URLs, one thing you need to take care of is 301 redirection. Every page from “Domain A” should now point to “Domain B”.
DomaninA.com/123.html should 301 redirect to DomainB.com/123.html
You can verify the same using an online redirect checker. Here is one such redirect checker- http://www.redirect-checker.org/
Setting up Permanent 301 Redirects
Setting up a permanent 301 redirect is very important for both SEO and user experience. This allows you to redirect users and search engines to your new site. In other words, whenever someone lands on one of your old posts or pages, then they will be automatically redirected to your new site.
To setup a permanent 301 redirect, you need to connect to your old site using FTP and edit the .htaccess file. This will be located in the same directory as your wp-includes or wp-admin folder. Open the .htaccess file and paste the following code at the very top:
RewriteRule ^(.*)$ http://www.newsite.COM/$1 [R=301,L]
Note: Replace newsite.com with your domain in the above code.
Once you have applied these changes, then visit your old site. It should automatically redirect you to the new site. If it doesn’t, then it means the redirection is not setup properly.
Step 4: Notifying Google About the Change
Login to your Google Webmaster Tools account to submit a change of address. Basically click on your site and look at the left menu under configuration. This allows you to notify Google about your new site and the transfer. Yes, you have to verify your new site, so go ahead and do it.
Google Webmaster Tools Change of Address
Step 5: Notify Users
While the 301 redirects do the job, it is always good to make a public announcement about the migration. You can do this by simply writing a blog post on your new site. This can be helpful in a lot of ways. First and foremost, your users are more likely to remember the new domain once they read about it.
Second, you can ask your users to let you know if they see any bugs. This can be very helpful because you alone cannot test your site in all different type of browsers and system environments. Besides it always help to have a fresh pair of eyes looking at it.