It will check periodically over wifi whenever you reboot the phone as well as when it has been on for a while. Updates roll out in stages that no one has been able to adequately explain. It will come to you eventually.
If you ever go to settings and to bottom option "about tablet" and then "system updates", you'll notice it tells you the last time it checked. It checks generally once per day, if it is powered on.
When the tablet has downloaded the update and is ready to install it, you'll see a notification pop up. You don't need to do anything to check or download it, the tablet will do all of that by itself in the background. You just have to give the final OK once it's ready.