Although the update for the latest version of the Android, namely v 4.3 has already made its way to Nexus Devices and Google Play Editions of the S4 and HTC One, still majority of the people have been waiting for their turn to come.
The Cyanogenmod team famous for their Custom ROMs is busy embedding the features on Android 4.3 in their latest nightly build for their most recent release the CM 10.2.
Though the update is minor, still some things are useless.The Multi User support has been revamped and also the Notification gestures. Also to note that OpenGL ES 3.0 is now supported which results in better graphics, and also a low energy mode for the new Bluetooth v 4.0.
So until the updates come to your respective smartphones, the third party Custom ROMs are a only way to enjoy the leisure of Android 4.3. have the CM 10.2 Nightly 10.2 here, but also keep in mind that it ha many bugs that need to fixed as off now.