As confirmed earlier, Asus starts rolling out the Android 6.0 Marshmallow update for its ZenFone series smartphones. The first device getting the Marshmallow update is ZenFone 2 Laser (ZE500KL) and the OTA (over the air) update started to distribute to the device with build number 18.104.22.168_M3.6.44. As the update roll out in phases, it will take about one week to get the update across devices.
Note that the update will replace three ZenUI apps, such as Asus Messenger, Asus Mail and Asus Calendar to Google Messenger, Calendar, and Gmail. In addition to that, many apps will no longer be pre-loaded once you upgraded your ZenFone 2 Laser to Android 6.0 Marshmallow, such as Asus Backup, Data Transfer, Photo Frame, Google+, etc.
1. Before starting the software update, please free up space on your internal storage. The upgrade requires more than 2GB free space in the internal storage. Once you upgraded your device to Android 6.0 Marshmallow, internal storage will decrease slightly.
2. If you did not receive the update notification on your ZenFone 2 Laser (ZE500KL), check it by going to Settings > About > System Update to update manually.
Once you upgrade your Zenfone 2 Laser to Android Marshmallow, your phone become incredibly fast and fluid. You will get new features like personalized app permission model, Android Pay, Doze mode for better battery life and more. (Source)