Changing/Switching Domain Name, How to do the same?

I build a website, wrote plenty of articles, built plenty of backlink..etc, the sites get some traffic from Google and from Backlinks and few click on adsense etc, as this was my first website I didn’t do any keyword research and used a an average sounding domain name

Now I want to re-do/re-brand the website, use a CMS (the earlier one is static) and use a different TLD domain name, I want to know how should I go about doing the same and how can I minimize damage, also will the content on the new site will be seen as duplicate content by Google? Should I keep the old site too? Also anyway the new site can replace the rankings in Google for the old site?

 

Create 301 redirects from all pages on the old domain to the new domain. It's not a perfect solution but will at least minimize damages.

 

Thanks, but if I keep both websites won't the content on second site considered as duplicate content

 

Yes, it will be considered as duplicate content; moreover, may be site will be not able to get ranking for targeted keyword. Due to panda and penguin updates.