You need go to the home screen first, if you aren't already there. Then, you go to Settings, then General, and then About. There it should list a bunch of information, including number of songs, photos, apps, and other stuff. Scroll down and you should find what version your device is running.
And in case you might not have known, if you want to update your device, just go to Settings, then general, then Software Update. If you have the latest iOS release on your device, It will say you are up to date.
I hope this helped you!