Asus Zenfone 6, ZenFone 5 and ZenFone 4 are now being updated to Android Lollipop

While Asus is pushing the updates over the air (in phases) to all three ZenFone models, users can also manually download the necessary files. Asus notes that Android Lollipop doesn't support some of the apps pre-installed on its smartphones, so these will be removed when the update is complete. At the same time, other apps will be added in the system update. You can see all the changes, and download the system update files at the source links found at the end of this article.
Asus is also planning to bring Android Lollipop to two tablets: the PadFone S, and the PadFone Infinity 2. Both should get the update sometime later this year.
source: Asus (ZenFone 4, ZenFone 5, ZenFone 6) via GSM Arena