Problem occurs due to mirror sites?

I have a site but by mistake i don't know about the mirror site , i am update whole content to my new site, but it was for previous site so, whenever i update my content in previous site then 1 one shows mirror site according to Google or search engines so what problems i will face in seo or search engine optimization or i can say to increasing ranking tell me the exact answers no spamming please thanks for the favor.