How do I upgrade the Android OS on my Galaxy Tablet Tab2?

I would suggest following this guide: https://support.google.com/android/answe...

Do note that the Galaxy Tab 2 is an incredibly old device, and the latest version of android that it supports is 4.1 (Jelly Bean). You could probably try using a custom ROM for the Galaxy Tab 2 which might be using a later version of Android, but that is a difficult process and you definitely wouldn't be getting any modern version of Android. You should also consider system performance since newer versions tend to have more features than older versions of Android which might slow down the device, so do this at your own risk.