They can't able to use windows 10 because so many bugs are there.I will tell you how to downgrade your phone windows 10 to windows 8.1.First, you have to open the google and type on NSU for retail version 4.3.2.In the page view so many sites.You will download NSU for retail (or) Nokia software updated retail 4.3.2 and download that.
HOW TO INSTALL NOKIA SOFTWARE UPDATED RETAIL 4.3.2 ?
First, go to download and click the file what you are downloaded.I will tell you how to install folder and click install and those drives are installed in your computer.It will download some files to take some time that is estimating on your internet speed in your computer.The files are installed it ask next and cancel.You click on next and accept and it will show you what files are downloaded on your computer.It shows you the page shortcut for a desktop option if you want the icon on desktop mark the option and clicks next folder is installed.
After connecting it will show you '' can install software version'' and click on install.It will show yo some details about that and click continue.The file will download to your phone.It will take some time is depending upon your internet speed and click install and your phone is restarted.
After installing some files your phone can restart in that time don't click ignore and don't disconnect your USB cable.After completed you click on finish the windows 10 is a rollback to windows 8.1.