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Older phones only recieve two major software updates @sp2020
What is the current firmware on the phone ?
Was it supplied directly by Samsung or via a mobile phone contract from a Network ?
Due to the release date of your phone it's probably yours has reached it's full update cycle.
It should however hopefully still get security updates.
The only other possible options are a Custom Rom.
Xda-developers.com is a good site to visit to learn.
Using a Custom Rom can bring about an unstable phone or it may not work properly if the process glitches or the wrong Rom is used.
A person takes full responsibility if they perform this process and do so at their own informed decision. Samsung would levy a charge to put this right.