You would know if it had been updated - you would have given permission for it to install. What version do you have?
Settings - about tablet (at the bottom) - version
Mine is Android version 5.1 and it recently updated from jelly bean to lollipop. That caused my tablet to run very slowly, hang, freeze, battery drain, all sorts of frustration.
I solved it easily enough by resetting it to factory default. It was 'box fresh' but running lollipop and now it is better than ever.