This security and maintenance release features 26 bug fixes in addition to two security fixes. Because this is a security release, it is recommended that you update your sites immediately. All versions since WordPress 4.7 have also been updated.
WordPress.org already started automatic background updates that do not require you to do anything, but it may take some time for them to get to your website. If it does not update automatically, either do it yourself (and don’t forget to make a full backup first!) or contact Dusk Owl for help.