How can i go back to the original firmware ?

[wf]

Could somebody please help me with it?

[_alexdon_]

http://talk.sonymobile.com/t5/Xperia-Z-ZL-ZR/How-to-manually-update-downgrade-root-2013-Xperias/m-p/...

Check out this topic.

[Thommo]

This thread on XDA has all you need here