If, as me, you bought your Meizu Pro 6s on AliExpress and you get stuck with Flyme 5G (chinese A-ROM actually, tweaked to look like a G one), you would probably change it for the REAL Flyme 6G, the current beta version published by Meizu.
It is possible, I just did it this evening on my Pro 6s. How to proceed ? It's quite easy actually, and safe.
1. Enable the root permissions :
Head to Settings --> Fingerprint and security
Scroll down a little bit and look for Root permissions click it and follow what it says. IT WILL REBOOT - IT"S OK!!
Put the file pro.sh in your phone root directory. Do not execute it (for now), wait for the step 4.
3. Download the latest Flyme 6G snapshot
Important : Pro 6 and Pro 6s share the same rom : you can install the Pro 6 rom on your Pro 6s safely.
Put the file update.zip in your phone root directory.
4. Download Terminal Emulator from the Play Store
Run it, and type the following commands in the phone terminal :
su sh /sdcard/pro.sh
Now, your phone should restart in the recovery mode by itself.
5. Proceed your upgrade the normal way
Check "system upgrade".
Notice : no need to clear your data. You can uncheck this option.
Then press "Start", wait for the phone reboot, and enjoy your Flyme 6 Global on your Pro 6s ;)