Hello, I bought the phone M3s in chinese website with already installed Flyme 5.1.5.0G.

I would want to install the version Flyme 6.3.0.0G which is available for the phone but,
when I launch the file (update.zip), a black screen tells that the firmware is corrupt.

Is there a detailed way to overcome this?

If the user buys the phone with Global version, it's not clear why he cannot upgrade to the same line of firmware.