This security release features four security fixes. Because this is a security release, it is recommended that you update your sites immediately. All versions since WordPress 3.7 have also been updated.
WordPress 5.8.3 is a short-cycle security release. The next major release will be version 5.9, which is already in the Release Candidate stage.
You can update to WordPress 5.8.3 by downloading from WordPress.org or visiting your Dashboard → Updates and clicking Update Now.