mac os catalina mac pro 13 2012 upgrade to high sierra

the suggested way to upgrade which is click on the apple logo doesn't show the path needed to upgrade. The app store searching on high Sierra yields nothing. there are sites on the internet to do it but they require my credit card details which im reactant to provide.

Question 1 I gather I can upgrade to V 11 is this true?

Question 2 How do I do the upgrade?

cheers

Ewen