Hi everyone, Forgive me if ive done this wrong as i have only just joined the forum. I need help with Panzer corps 2 , my problem is how and when can i upgrade my planes. I am running the kursk battle as the Germans, my Armour,Infantry etc wil upgrade to better and later units,but my aircraft ie Me1...

Sorry if this is wrong place but im so frustrated i am playing panzer corps 2, my question is why cannot upgrade my German aircraft from bf109 or stuke dive bomber to somthing else? There is the option to upgrade but there is no upgrade help please