old posts

I am working on redesigning one blog layout. There are older posts, not properly SEO optimized. Should I go through all of these and optimize them now or it doesn't matter?

I had 2 blogs in the past for tests, just for put in practice what I was learning. Now I'm planing a new website and still have beginner doubts. My doubt is if I rewrite a post entirely, improving their quality and increasing their length, do I risk losing Google rankings or is it improve it...

As from your experience should I update old post (from 2014)? I have a site with about 100 posts, for the example, let say that the old post, 50 for our example does not have inner links and external links, tags, h2 etc, it was a lot of text without really organizing it… Should I...