You can get the new firmware and upgrading method from the following link.
After upgrading success, please check the device as following:
Go to Settings
Go to About device
The "Baseband version" should be "pub-a10-zhpubhost1.8"
If your device already "pub-a10-zhpubhost1.8", the means your device already build-in newest firmware, you no need use this firmware.
If your firmware was damaged, you can use this firmware to restore it.