You could update your device via your PC. Just follow the steps below and you should be ready to roll.
1.0 [Preparation of your PC]
Download the ADB Tool HERE.
Click on the setup executable and type in "Y" for all the entries. (for the prompt on driver installation, simply click "Next", "Install", followed by "Finish").
1.1
Download the ASUS Software Update HERE.
Once completed, move the update file to C:\adb (where C: is the root drive where the ADB Tool was installed at).
2.0 [Preparation of Device]
Turn off your phone.
Press the "Volume Down" button followed by the "Power" button.
Keep holding the two buttons until the recovery screen appears, then release both AT THE SAME TIME.
Plug your phone into the PC.
On your phone, press the "Volume Down" button to select the option "apply update from adb".
Then, press the "Power" button once to select.
3.0 [Flashing]
Open the command prompt (Windows Key + R, type in "CMD" and enter).
Type in cd C:\adb (take note).
Then, type in adb sideload "downloaded file name".zip
4.0 [Finish]
Upon completion, make sure that the option "reboot system now" is selected on your phone.
Then, press the "Power" button once.