To get Android 9.0 on a KitKat-era phone, you need a – a community-built version of Android. The most popular choice is LineageOS 16.0 (the custom ROM based on Android 9 Pie).
For certain devices (e.g., Samsung Galaxy S4, Nexus 5, HTC One M8), the developer community may have created custom Android 9.0 ROMs like LineageOS 16.0. This requires: upgrade android 4.4.2 to 9.0