Share your experience!
There are 2 ways to do so
1. contact your local Xperia care
or
2. use flashtool
@reilly
1. http://support.sonymobile.com/global-en/contactUs/
2. http://talk.sonymobile.com/t5/Xperia-Z-ZL-ZR/How-to-manually-update-downgrade-root-2013-Xperias/td-p...
/t5/Xperia-Z2/How-to-manually-update-downgrade-root-2014-Xperias/td-p/593459
Please do not create other threads as solutions are available:
/t5/Software-Updates/Downgrade-Z3-compact-and-others-from-Lollipop-to-KitKat/m-p/955640#U955640