https://www.theverge.com/2018/9/17/17869316/apple-ios-12-iphone-ipad-download-available-now

iOS 12 — the latest edition of Apple’s software for its iPhone and iPad devices — is now available for all users to download, assuming you have a recent-enough device. (Check the list to see if you’re eligible for the update.) To install, go to the Settings app -> General -> Software Update, and you should see the prompt to update.

Introduced at WWDC earlier this year, iOS 12 is first and foremost focused on improving performance to make iOS feel faster, especially on older devices that have become more sluggish over time.