Downgrading a Sony Z3 Tablet Compact tablet SGP621 from lollipop 5.1.1 to kitkat 4.4.

Hello

I want
Downgrading a Sony Z3 Tablet Compact tablet SGP621 from lollipop 5.1.1 to kitkat 4.4.4

SGP621

any help ? or video youtube

i want easy way pls .