Best method for moving content from one site to another?

Hello. I have a blog that was getting around 500 unique visitors a day. I decided I didn’t like the layout, the look, and the domain name I was using.

I began working on a new site (new look and new name). I kept the old site up and running while working on the new site, which was in it’s own directory.

Now that I’m close to finishing the new site and making the switch, I’m concerned with a couple of things:

1) I would rather not lose traffic from my old blog, so I guess doing redirects would make since. Do I have to redirect every page manually or is there a quicker way.

2) Should I just delete the old site altogether as to avoid getting punished by the search engines for having duplicate content?

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There are articles on switching domains and switching websites but I can’t find the answers to these questions. I’m just confused on whether I should just delete the old site and move on, or try to save some of the old traffic by redirecting it to my new site. And if I chose to keep my old site live, how do I avoid getting punished for having duplicate content?

Thanks for any help