Download latest update.zip and move it to root of your SD, so it is not in any kind of folder. Now shut the phone down and press Volume Up + Power. Select “Clear Data” and start the “Upgrade”.
It will reflash the system files + remove all of your apps and so custom settings.
To do full wipe data of your Meizu, we can use phone data eraser tool. It helps us wipe all personal data like contacts, text messages, photos, videos, user names, passwords and all personal info without recovery. So there is no need worrying about information leaked.