If you want to apply the update, you’ll unfortunately need to use LG’s Update Tool, which is an application for desktop Windows. So a PC is a must for updating. The update’s rollout isn’t of the over-the-air variety, that would have simplified things a lot for Optimus 4X HD owners.
That said, if you’re determined to apply this update on your device, you won’t find it especially hard. Just follow the very detailed update instructions from this page.
The update brings with it all the wonderful enhancements of Project Butter, a constant frame rate by way of Vsync, improved overall responsiveness, expandable (and actionable) notifications, Google Now, voice typing without an Internet connection, support for Wi-Fi Protected Setup (WPS), and more.
Obviously, the update is worth performing as soon as you have half an hour free, so why don’t you check and see if it’s available for you?