If you do not receive the notification for the OTA update on your phone, you may check it manually by going to Settings > About > System Update. You can also download and install the 15.0405.1711.76 update manually on Zenfone 4 as given below. Check out the guide below to know how to download and install the Oreo update manually on Zenfone 4 ZE554KL.

Release Notes (ZE554KL_ WW_15.0405.1711.76): Tech-savvy users can install the update manually by downloading the update file (V15.0405.1711.76). For example, if you are out of Wi-Fi network area, you may want to install the update manually. Note: If you prefer manual installation and before proceeding with below steps, back up every data you have on the phone. Also, make sure at least 3GB free space remaining on the SD card. Also Read: How to Unlock Zenfone 4 bootloader officially

How to Update ZenFone 4 ZE554KL to Android Oreo

  1. Download 15.0405.1711.76 update zip file for ZenFone 4 ZE554KL [download] (link not yet live) Note: Download correct firmware builds for your SKU. Check the SKU by going to Settings > About > software information > Build number and see the software version for WW, CN, JP, etc.
  2. Rename the downloaded firmware file to ‘update.zip’ and save it on your phone.
  3. Boot your phone into recovery mode (Switch off the phone and turn on by pressing Power + Volume Up buttons together) . 4. In recovery, choose Apply update from sd card and then select the update.zip file.
  4. After completing the installation, reboot your phone. (Source)