Zenfone 2 not upgrading android OS

[Sam_C]

Hi, I have a Zenfone 2 ZE551ML and somehow is stuck on android 5.0 and does not allows to upgrade

[il_Santo]

You have to manually update to android 6. Search support dite for correct rom

[Christine_ASUS]

Hi Sam C
First, I already deleted your previous thread. Please avoid any overlapping thread or message, which may disturb the mods and the users to solve the issue. 
Second, as il Sant mentioned, your current firmware version is the last version of Android 5 (Android L). To update to Android 6 (Android M), please backup the device data, download the OTA file on our official website and perform manual update. Please read the precaution carefully and avoid to download the OTA file for other countries' SKU (WW/Brasil/JP...).
#Manual Update (Download the OTA file into the root directory, aka the outermost place, of the internal storage.> Reboot>Tap the system upfate notification)
https://www.asus.com/support/FAQ/1009748/
Besides, if you still prefer Android 5 interface/system design, you can downgrade from Android 6 to Android 5 by the downgrade file on Firmware Spot.