User blog comment:Mathmagician/Why Dart Traps?/@comment-152.26.69.34-20120111125133/@comment-4674838-20120112031138

Terraria updates automatically (for free) if you buy it on Steam. So you will get the most recent patch (newest version). As far as I know, there's no way to update it manually. You just have to rely on the auto-update feature in Steam.