It may seem obvious that you ought to upgrade WordPress whenever upgrades are released. If security was the only rationale to do, it would be an EXCELLENT one. But it’s not the only reason — check out the other benefits of making upgrades a regular part of your work in my post — https://jakegroup.com/blog/the-importance-of-upgrading-wordpress/
Goal-oriented, analytics driven, open source web engineering with a WordPress slant.