There are two ways Asus update:
- Using recovery (to update installed OS)
- Using Asus Flash Tool (to recover Asus update)
If you want to install an Asus update using recovery – download the official update, reboot your phone or tablet into recovery mode and click “Install update from SD card”.
To flash Asus firmware with Asus Flash Tool you’ll need PC installed drivers, full guide how to flash Asus is here.