How to upgrade from 5.0 to 5.3

Hi all, thanks for your help.

I have Apple TV 5.0.2 and wish to upgrade to the latest 5.3

If I go to settings/general/update software I get a message that says I have the most recent one. Which is not true.

I have aTV Flash (black) 2.3

How can I upgrade?

 

Thanks for your time and help.

 

Use seasonpass. 5.3 is tethered at the moment but it was written that it will be untethered within a week.