Firmware upgrade failure - GL-AR750S-Ext

I have a Slate Dual-band Mini Router GL-AR750S-Ext.
I have tried online update and local update firmware, but it fails each time.
I have 3.1, and am trying to update to 3.203.

If you have 3.104 you should upgrade to 3.105 first. Then from 3.105 you can upgrade to 3.203.