Android Marshmallow is now available for your Samsung Galaxy Tab S devices.
This update is expected to fix any bug that was present in the previous Android version, It would also bring to your device Android's cool Marshmallow features
which includes an optimized ui as well as Google Doze mode.
Without wasting much time go to your Settings on your device and download the Marshmallow update.
If probably this update has not yet arrived for your device then you would have to wait for some days and you should recieve it.
Note that Android 7.0 Nougat is still rolling out to more devices as the time goes and probably it would be rolled out on the Samsung Galaxy Tab S devices in the near future.