I know its an older post but duplicate content has become a big issue in IT world.Duplicate content always affects your ranking and it may also ban your site from web.Yes if you will put the pure and original content then your site will definitely rank.
Hi, If your content are duplicate and ranking is good, and you want to change the content so that's on not big issue if first time get down ranked your website, so second crawling are get good ranking and most effecting better then before.
Duplicate Content is not a good thing for a website ranking anytime google can punish you so it would be better if you change your website content and never use duplicate content you can check your content before you use...
I think its very difficult to recover your rank through deleting duplicate content. You need start from zero to improve your ranking.
Delete the duplicate content and increase the % of unique and quality content then its works. Also try to get the backlinks from high quality websites. And keep updating our websites with on-page factors as well as fresh content.