i copied a live site content to a  new installed DNN7.3 manually, and replace the old site with the new site (with same Domain) this cause all of URLs are changed.

for example the 

http://rayeshmand.ir/News/one-of-the-largest-onlin... (old url)

change to 

http://rayeshmand.ir/Detail/category/1/one-of-the-... (new url)

now when a related keyword is searched in Google the old URL is found and when user click to the URL go to the 404 error page in new site. 

Whether this has a negative impact on SEO? 

What should I do to solve it?

Can I use 301 redirects?

Or should I wait for Google to index the contents from beginning?

Regards,

Mohammad