http://www.asus.com/th/Phones/ZenFone_4_A400CG/HelpDesk_Download/

เลือก > Android >Firmware

ASUS ZenFone4(T00I) software Image: V6.5.24 (Android 4.4)
for CHT SKU only*
Improvement:
1.System upgrade to KitKat 4.4
2.Call Guard
3.Filter effects for videos
4.Reply via Call-in SIM card, system will auto select the right phone number via the call
5.Full dual standby with two SIM cards (applies to dual SIM models only)
6.Do Not Disturb mode

Steps of Update:
1.Check software version of your device**
2.Download device software and Update SOP (From “Manual” Item)
3.Only apply to same SKU update, Example: WW->WW, CN->CN, TW->TW.
4.Software update cannot transfer the software SKU and downgrade the software version.
5.Wrong SKU may cause update failure, please update the same SKU version only.

*How to know the device model?
Path: Settings->About-> Model number
Example: ASUS_T00I
**How to know the device software version?
Path: Settings->About-> software information->Build number
***System upgrade may cause part of data missing, please buckup your important data before system upgrading.