Can't update OS & Can't update payment info, vicious cycle!
I am trying to update my wife's computer since she never has since she bought her MacBook Pro in 2012. We are currently running OS X 10.8.5. I am trying to upgrade her OS to Mojave but when I click "GET" and enter my Password, I get a pop-up that says Verification is required & I need to approve my billing info in iTunes. So I click on the Billing Info option & I get another pop-up that says Software Update Required and says to make changes to my payment info I have to upgrade to the latest OS. I click Learn More and it sends me to this link:
About App Store and iTunes Store availability - Apple Support
This basically says, "if you can't change your payment method, then you need to update your OS". But if I can't update my OS without changing my payment method, then what am I supposed to do???
Please help!!!
MacBook Pro, OS X Mountain Lion (10.8.5)