3 tend to be really behind in rolling out updates for phones locked to their network. Its crazy! My phone is on EE, so I dont have to wait for it to get updates too much which is good.
I don't know if this will help, if your phone is locked if you have 3 app on your phone they should be somewhere in that app that will tell you about unlocking, if not phone 3 and ask them to unlock your phone by law they have to do this.
Since 2014 all three phones come unlocked and that is still the case but they run three firmware which is unfortunate for getting updates at the same time as everyone with sim free phones.
When you get a new phone, buy it from Samsung and change your three contract to sim only. It saves money and ensures that you will be the first to get updates in your country the majority of the time.