How to inform Google that http://www.oldcompany.com is now http://www.newcompany.com, and transferring the rating from the old site to the new one.
Here is how you should proceed: create a Google Webmaster account here and verify and let Google verify ownership of your domain: https://www.google.com/webmasters/verification/
Then do the following:
If you’ve moved your site to a new domain, you can use the Change of address tool to tell Google about your new URL. We’ll update our index to reflect your new URL. Changes will stay in effect for 180 days, by which time we’ll have crawled and indexed the pages at your new URL.
The change of address tool is safe, because only verified site owners can use it. You can check the tool at any time to see the information provided to Google about your domains.
Note: If you’ve specified a preferred domain for your original site, you should also set it for your new site.
Important: In order to use the change of address tool, make sure that you’ve added and verified both your old and new sites, and read the guidelines on moving your site to a new domain. You should be especially carefully to use 301 redirects to tell search engines about the new location of your pages. In addition, make sure your original site is not a subdomain (for example, http://newsite.example.com).
1. On the Webmaster Tools Home page, click the site you want.
2. Under Site configuration, click Change of address.
3. In Step 4, in the Select a verified site list, select the new site.
If your new site doesn’t appear in the Select a site list, check the following:
* Make sure you’ve added your new site to your Webmaster Tools account, and verified ownership.
* Make sure that your new site is not a subdomain. For example, you can use http://www.example.com, but not http://www.example.com/newsite or http://newsite.example.com.
* If you’ve specified a preferred domain for your new site, only that preferred domain will appear in the list. For example, if http://www.example.com is not appearing, make sure that you have not specified http://example.com has your preferred domain.
If you submit a change of address notice redirecting traffic to your new site (www.example.com), you can’t then submit another change of address notice specifying that the content on http://www.example.com has moved to a new site.