First of all, you turn off your android device and make sure you have install fast boot tab on your windows.Hold done the volume down button and the power button at the same time and you will get and download mode.
Now click detect your device and connect your PC (or) Laptop using USB cable.
Install fast boot tab on your windows PC otherwise your fast boot tab doesn't recognize your device.After connection it shows a cable make in the windows button right corner it makes tick indication connection right now your device work in the ap fast boot.
First, you can download one file called hammerhead-ktu84m.After download,open the application it has a Zip file to the main file you have download it.First, make a new folder in your windows PC create name android once create name android once create that folder once you can install Kitkat 4.4.3 in that folder.
Extract the Zip file to the main file to the android folder.All you need is once you have done all these things click on shift and right click on that android folder and you will get an option open command window here click on that option.The command prompt on a here folder.
Now type flash all bat and click enter and type flash-all-best and enter.It based on your connect and your device.Once connect and disconnect it will install everything just it take two-three minutes and in that time you don't disconnect your phone.
This procedure is very easy to install android lollipop in the same way downgrade KitKat 4.4.4 (or) 4.4.3 whatever maybe but it is KitKat version.After complete just click on power button it turns to KitKat and everything will be working good.This is the best downgrade.