Manually update your phone from Android 4.4 to Android 5.0

You have to manually update OS from Android 4.4 to Android 5.0 for models listed below:
ZenFone series: A400CG, A450CG, A500CG, A600CG, A500KL
PadFone series: PF500KL, A86

Please update your phone manually by update launcher downloaded on ASUS official website.
Please refer to "b. Manual Update" section in link below.
https://www.asus.com/support/faq/1009748

Note: Before update to Android 5.0, please tap [Check Update] in [Settings] -> [About] -> [System update]
to make sure the firmware on your phone updated to the version of Android 4.4 listed below.