You can either auto-update or manually update your firmware to be able to use the latest version on your device. Check out the following steps to know how.
Note: Before updating, connect your phone to a power outlet using its AC adapter or make sure the phone has at least 15% battery life.
How to auto-update
Connect your phone to the Internet.
Tap Check Update in Settings > About > System update to check if the firmware is latest.
If there's an available newer version, follow the steps onscreen to update your phone.
You can also go to ASUS' official website to download the latest firmware and its instruction manual.
Please ensure that the firmware SKU you'll download is compatible with your phone, eg., WW -> WW, CN -> CN, TW -> TW. An incorrect SKU will lead to update failure. Also, downgrading your firmware cannot be done, eg., V22.214.171.124 -> V126.96.36.199.