Android 4.4.2 has not received a security patch since 2015. Upgrading to 9.0 gives you patches up to 2021, plus modern security features like encrypted backups and biometric authentication frameworks.
Check the XDA Developers forum for your specific device to see which ROMs are actively maintained and have the best compatibility.
There are three primary ways to upgrade your device, ranging from the simplest to the most advanced: upgrade android 4.4.2 to 9.0
Android manufacturers typically provide major OS updates for only 2 to 3 years. The gap between Android 4.4 and 9.0 is five years and five major versions. The hardware drivers (the software that tells the OS how to use the processor, camera, and screen) for KitKat-era chips (like the Snapdragon 400 or 600 series) were never written for Android 9.0 by the manufacturers.
You cannot simply download an upgrade file to your phone and install it. You must prepare your PC and your phone using specialized tools. 1. Full Data Backup Android 4
Remember: XDA Developers is your best friend. Search for your exact device model before typing a single command. Good luck, and welcome to the world of gesture navigation and adaptive icons.
This is the safest method, but the least likely to work for a jump from 4.4.2 to 9.0. It's always worth checking first: There are three primary ways to upgrade your
From KitKat to Pie: Is It Possible to Upgrade Android 4.4.2 to 9.0?
Connect your phone to the computer while still inside TWRP. Your computer should recognize the phone's internal storage.
Upgrading across five major generations of Android brings massive changes to your device. Why Official Updates Are Impossible
Requires requesting an unlock key directly from the manufacturer website using ADB commands.