you download from flyme telegram page the firmware 8.1.5A, a big zip file to the root folder of your phone.
if you have created a flyme account, disconnect it
power off
boot by pressing volume up+power butttons.
you follow instructions on first post of this thread.
dosconnecting flyme account os to prevent some issues after tiu upgrade.
it works on mine, even the install of google services.
root os not Working, i can clock on root button but my phone didn't reboot.
i reboot it but no change