The content that is there is there, it is OK. Don't change it.
Add new content and concentrate your link building on the new pages.
Don't worry too much about Copyscape. It is easy to get paranoid about using it because so many people seem to do so. Add content to your site that is relevant to your readers and to your purpose. Best, of course, is content written specifically for your site, but there are other options. One that works just fine is to inject new content into PLR articles using Jon Leger's ArticleBuilder.net this works by adding content to a page and rendering the content 'unique' again.
I tried this as an experiment before Jon relaunched ArticleBuilder a few months back and it works sweet as a nut. Articles that were years old, sitting on my hard drive and hundreds of websites acted like young maidens attracting spring youths.

by the addition of a few sentences of new, relevant and decently written content - even though the content I was adding was itself drawn from ancient and well used sources. ArticleBuilder makes fresh unique content and works a dream!