A blog post can be updated in a number of ways. Sometimes small changes are made that do not require a full new article to be written.
Other times larger changes may be made, such as adding a new section or changing the focus of the article.
When deciding whether or not to update a blog post, it is important to consider the purpose of the blog and whether or not the change will help move the blog forward. If the change is minor and will not interfere with the overall goal of the blog, then it may be appropriate to make the change without any further notice.
If, however, the change is more significant, then it may be necessary to provide a more detailed explanation and/or wait for feedback before committing to writing a new article.
Ultimately, it is up to the individual blogger to decide when and how to update their blog posts. However, providing accurate information and ensuring that changes will not negatively impact readership should always be a priority.