As I previously say , I personally remember that’s this option was also available in Flyme 5 don’t remember exactly the path though. Somewhere near accesibility or dev options (after root) probably.
If you want to upgrade you need to determine which version are you currently running (G - Global , A Chinese Y Yun OS )
Here you will find all the firmwares https://downloads.meizufans.eu
Download the one for your phone
- Put the update on the root of your phone
- Shutdown the phone
- Press Power + Vol Up
- Choose how to install update you keep all your data , Clear Data you lose all it does a fresh install.
In any case save the update already available on the root of your phone now for backup if new build have issue of draining battery or other bugs.