Do bear in mind that this particular firmware is made available in the form of an Over The Air (OTA) download, where it will be a massive one to boot. We are talking about approximately 940MB of content that needs to be downloaded prior to installation, so it would make plenty of sense if one were to ensure that this is done over a Wi-Fi connection rather than having it eat into your data plan needlessly.
Right now, it seems as though the Meizu servers are overloaded, so it is far from surprising to find out that the download process itself is rather slow. The best thing that users can do at the moment to ensure that you can get the update in a hassle-free manner? Perhaps being patient would work, as you wait it out for a few hours, or perhaps even a day before trying. The Flyme 5.0 version will deliver a flatter user interface, accompanied by refined icons and animations, improved battery life and overall stability and performance improvements.