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.
Released in early 2014, the ZenFone 4, ZenFone 5, and ZenFone 6 are still available to buy around the world, despite the fact that this year Asus introduced its second-generation family of ZenFone handsets, including the ZenFone 2, ZenFone Zoom, and, more recently, the ZenFone Selfie. All the Asus smartphones introduced this year are running Android Lollipop out of the box.
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