Note 4 won't update? Is there a solution? Is this a security risk?

I bought a Note 4 on Ebay.
New in box.

I figured that if I didn't like it or it didn't work, the kids could use it for games and drawing (and a s a remote control).

It runs Android 5.0.1, but I understood that this phone still received updates.

When I go into Settings-About Device-Software updates, and tap 'Update Now' , nothing happens.

I would have liked some of the more advanced functions and Google Assistant.

My questions:
Can I still get an update somehow?
Is it a security risk if I don't, or can I use the device as is?

Sorry if I sound clueless, I come from iPhone and I have unlearned all things Android.

via International Skeptics Forum http://ift.tt/2eJaWDM