Will "renewing" my wordpress posts damage SEO.?

[David]

I have 15 large posts on my wordpress site. I'm ranking in Google okay for search terms relating to the content, now I know a few others have copied/quoted the content online but this isn't an issue because Google clearly recognises I'm the owner due to using webmasters and Google Authorship and submitting it first.

However what happens if I now go in and renew my content - Will Google now see these as brand new content and put me in last place then as regards "the first to post the content"?
Please offer me some advice as my posts are really in need of an update regarding hyperlinks, pictures and content changes but I don't want to do it in case my rankings drop.

Really appreciate any advice or feedback, thanks.