Please try the following steps.
① On the home screen, tap 「Settings」
② When Settings appears, tap 「General」
※If an update is required, a number will be displayed in a red circle next to 「General」.
If you wish to proceed with the update, please tap 「General」 and then proceed to 「Software Update」
③ Tap 「about」
④ The number next to the Software version is the version of your device.
※If the software version is older, please update your device.