how do i change security questions

If you can't remember your answers see if you can reset them : If you forgot the answers to your Apple ID security questions

If you can’t reset them yourself you could try contacting Support in the country where you live (and which is therefore the country on your account) and see if they can reset them for you : http://www.apple.com/support/itunes/ww (click on your country's flag, the country where you live, and which is therefore the country on the account ; click on Contact Support towards the top right ; click on Get Help under 'Talk To Us’)

But Support might not be able to reset them for you, from Security and your Apple ID : ‘Without proof of your identity via security questions and other carefully selected criteria, Apple Support can't help you reset a password or perform any other actions on your account.’