I don't delete but I do edit them to add in some links that point forward to later posts. Revisiting my archives does not only allows me to update the information there, it sometimes provide me with inspiration of what to write.

sometimes,i will edit the old post,because i have to notice the readers some informations

There may be a good reason to delete an old post in the future and I'm sure there will be a good reason to update posts in the future too.

If there are a lot of edits to the post though I would probably put 'UPDATE' or whatever in the post and explain what was being updated and why.

Does WordPress re-ping if you edit?

@BeachBum – An update: is good way to do it, but the article would still rank in the search engines showing a snippet saying they were guilty?

Michael

I can't say I've ever thought about it, to be honest.

I moderate on a lot of forums. On all those forums we have rules in place that mean crucial details cannot be removed from posts, and posts cannot be deleted (unless they break a rule) We'll edit out contact details or surnames if needed, but that's all.

The reason for this is simple. Once posted, it's in the public domain and other authors around the Internet may have responded to your post or points in your post. Once that post is edited, everything surrounding it no longer makes sense. Authors are referencing points that no longer exist. There are other reasons why we don't edit the post, but that's the one that applies here.

Don't take that the wrong way. I would certainly edit a spelling error or grammatical error on a 12 month old post if I found one, or I would re-write a sentence so it makes more sense. What I wouldn't do is change the context of the post. Everything I said when I first posted it must remain, although I might edit the post to change how I say it in a bid to make the post easier to digest for my readers.