[Q] how to downgrade Htc 816 dual to kitkat topic

hi all
last week I had update my Htc 816 dua to lollipop for a lot problems i am facing i want to know how to flash back to kitkat
I prefer to official kitkat rom I had flash my previous sony xperia using flash tool so I want to know

1. if flashing htc phone need another flash tool software


2. a link to HTC 816 dual kitkat


3. and if there is a guide step by step would be better

Thanks

xda-developers