How to upgrade Samsung Galaxy S3 4.2.2 to android 6.0

[AC Question]

How to upgrade from android 4.2.2 to android 6.0.1 on a Samsung galaxy S III model SCH – I 535

 

[hallux]

Looks like you need a 3rd-party ROM to install Marshmallow on that device.

There's a forum here where you may find useful info toward that goal: Samsung Galaxy S3 Rooting, ROMs, & Hacks - Android Forums at AndroidCentral.com

I should warn you, doing this carries some risk that your phone could become useless if you miss a step or do something wrong.