The LG Optimus L9 for T-Mobile is receiving the Android 4.1.2 software update. This is the second time this update is being released for the Optimus L9 as it had to be halted the first time after causing battery and Wi-Fi issues for users. Users to updated to Android 4.1.2 the first time will receive the update again, which will hopefully fix the previous issues while adding new security features.For those who are running Android 4.0 Ice Cream Sandwich on their Optimus L9, the new update will introduce them to the world of Android 4.1 Jelly Bean with performance improvements from Project Butter, the Google Now digital assistant and interactive notifications.
The update is being offered (over-the-air) OTA and you can initiate the download once you receive the notification of its availability. Keep in mind that the update generally rolls out in waves, so it maybe awhile before in reaches all the handsets. You can manually check for the update availability by heading to Menu > Settings > About device > System update on your device and following the onscreen prompts.
source: T-Mobile