If you want to update or reflash the firmware of the Minix Neo X8 or Minix Neo X8-H Plus Android TV box, follow the instructions given below. The newest one available right now is called 004A firmware and it introduces myriad improvements over previous ones.
How to upgrade and flash official Minix Neo X8 X8-H PLUS ROM
If your TV box is not bricked then try this process. First of all, remove the SD card from the Minix if it is already inserted. Then install the update by going to the update icon in the application drawer. The installation process is automatic and the Android TV box will restart automatically.
If the above option does not work
You will have to use the Amlogic PC tool which can be downloaded from here. It is recommended that you use a windows 8 PC for flashing the ROM. During the installation process you will see Chinese but you can easily select English from the top menu. Restart your PC and download the firmware file from here. Extract it to find a IMG file and start the Amlogic PC tool too.
Make sure you Minix Neo X8 or Minix Neo X8-H Plus are off and connect them to the PC using micro USB OTG cable. Press recovery button on the device and Amlogic PC tool will recognize your TV box as shown below.
Click on the Start button and wait for the percentage to reach 100 percent. Upon process completion, the TV will restart but it will take longer than usual. Leave it untouched for few minutes and it will restart again.