App Store Trouble

Hi,

I purchased an upgrade for my mac computer from the apple website and was sent the details i needed to redeem it. However, everytime I try logging into the app store I get a message stating "This apple id has not yet been used with the app store, please review your account information". When I click on "Review" it then says "Software update required, to make changes to your payment information, you need to upgrade your mac to the latest version of macOS". When I click on "Learn more" it comes up with a hole page with numerous options and information and I have tried clicking on ones that maybe relevant and have done everything that is suggested to do but it still won't work 😟. Please help.

P.s: The current software on my computer is a 10.7.5 osx Lion, I am trying to upgrade it to 10.8 Mountain Lion.