Apple released iOS 9 two week ago to the public and just released a second software update this week.
Apple iOS 9.0.1 which was released last week, fixed an issue that caused iOS devices to freeze on the “Slide to Upgrade” screen during the software update process and an issue where sometimes alarms and times could fail to play.
Today Apple has released iOS 9.0.2 with several more major bug fixes and some improvements. iOS 9.0.2 fixes a settings problem that turns on or off app cellular data usage.
It also resolves issues that prevent iMessage activation for some users and iCloud Backup interruptions after starting a manual backup. iOS 9.0.2 also fixes an issue where the screen incorrectly rotates when receiving notifications. For a full list check out your devices update information.
You can install iOS 9.0.2 by going to your devices Settings > General > Software Update. Or you can connect your iOS device to iTunes and click Summary > Check for Update to install the update. The download size varies based on the type of iOS device you have.