How to update from Lollipop 5.1 to Marshmallow 6.0

[Android Central Question]

Hello everyone,
I have under my hands an old phone that I can use however I want. The current system is version 5.1 and what I would like to do is updating it. The thing is that I don't want any modern version but exactly the 6.0 . Moreover (I know it's not over yet I am sorry).. the 5th March 2017 there was a security update that prevented every mocking location app to work. My intent (for gaming purposes) is the one of indeed updating the system from 5.1 to 6.0 before that update.. I have no clue if this is really possible. But worth to ask at least Thanks in advance!

 

[belodion]

It would help us to answer if you told us what phone.

 

[Tigro90]

You are right.. it's a Sony Xperia Z1 (C6903). My apologies!

 

[belodion]

Welcome as a new member.

I don't think it would help in this instance to move the question to the Sony Z1 forum, since I doubt that there would be much activity there by now; so I'll move it to General Help & How To.