Just wondering how to update the OS once rooted

I recently rooted my Tab s 10.5 because I was getting fed up with not being able to use my SD card to store apps. So it went well no issues. However I was wondering, once a new version of Android is released i.e. Marshmallow is it possible to update to that OS and if so how do you do it? I would assume you need to download an .apk of it once its released and flash it over the same way I did when rooting? Anyway I figured I would ask if its something that can't be done then so be it. I'm happier with a rooted tablet running an older OS then an unrooted tablet with a newer OS.