how do I download osi 4.3 to my itouch which only has 4.2 version

how do I download osi 4.3 to my itouch which only has 4.2 version

I am trying to download the goPro app and it will not allow until I can update to osi 4.3

already got some advice, updated laptop itunes to most recent software and connected my itouch and request update

and I keep getting a message saying, you are fully updated.

please help