There's a way to switch a website without losing its rankings. Here are the steps to follow:
Check links that point to your old domain.
Collect a maximally complete backlink pattern of your old site (you may use
WebMeUp Backlink Tool for that) and put all the fetched data into a summary table. When done, you need to sort out the links that have little or no SEO value and
disavow them.
As for links from relevant and authoritative websites, you should keep them, as they will bring more link juice to your new domain.
That can be done either with
301 redirect or via direct contacting webmasters of websites where your links are placed on. Thus, SEO value of your old domain backlinks will pass to a new site.
Tell search engines that you have moved.
- submit your your old sitemap to Google and Bing (if you already have one, skip this step). That will make the search engines crawl your old site URLs, see that they have 301 redirects and change their index accordingly;
- fill out the 'Change of Address' form in GWT.
- create a new sitemap and submit it to the above mentioned search engines. This will tell them about any new URLs that were not present on the old domain);
- wait until Google Webmaster Tools updates and fixes any errors. That will be indicated in the
Diagnostics section.
All that will help you move a domain with the minimum loss of its online authority. Of course, you may lose some positions. However, if you follow the steps described above, you will be fine.
Hope you find this info useful.