Flyme allows you 3 ways to upgrade your firmware.
OTA stands for "over-the-air", meaning that a small file will be provided to update only the part of Flyme, which actually has been changed in the new firmware. While this sounds like a great invention, there are a couple of issues making the process complicated.
OTA updates can only be provided if your device is unrooted. Furthermore OTAs can be corrupted due to network errors, caused by the high ping times to the Chinese servers. Often this results in a bootloop.
Notification issues have been documentated as well, where users did not received the OTA.
As mentioned previously you can download the entire firmware (update.zip) from Flyme or our Firmware Archive. No matter where you download the file it will always be the same.
All you need to do after you have downloaded the firmware is to open the stock File Manager and click on the update.zip. A pop-up will appear allowing you to tick "Wipe user data too" (this will delete all your apps and restore default settings). Usually you can skip this and press the upgrade button, even if your device has been rooted (root will be lost, but can be recovered afterwards).
The device then will turn itself off and boot into the recovery where the flash will be done automatically.
This is the most secure and "old-school" way you can upgrade your phone. As with the file manager you need the full firmware. Open up the stock File Manager (or Windows Explorer in case you downloaded it over a PC for example) and move the update.zip to the root of the internal storage. Do not move it with 3rd party explorers as it often has happened that users tried to move it to "/", which is the systems root.
Shut the device off and then use Volume Up + Power to boot into the recovery. Here you can choose as well whether or not to wipe data.
The benefit of this method is that you can fix your device if its stuck in a bootloop, without the need of a computer.
Works just like the upgrading. Logically the OTA method is not supported.