how to ” downgrade ” to note 4 n910u?

i need downgrade a note 4 n910u 5.1.1 to 4.4, a colleague mentioned to me about a special firmware, using the hidden of 5.1.1,
and the latest "firmware" updates of Japan 5.0.1 .
and must use the pits.
I do not understand how it works.
someone could , please, explain me in detail as are the procedures ?
thanks very much!