I installed Resurrection Remix, a CM13 Android 6.0.x ROM. So far so good, I can make calls, Samsung Health works for pedometer and steps. Android 6 seems pretty fast, faster than Android 4 on the same hardware. There's a lot more customisation possible. All in all, a good move I think - so far.
Ok sooooo, nothing on TV so tonight is the night I dive in the deep end abd I am going to have a go at this.
Will report back to see if I am successful. (never done any of this before)