how to reset security questions

Sign into your Apple ID account (https://appleid.apple.com/#!&page=signin) and reset them there. And, if you have the option, then you may want to enable two-factor authentication--which provides much stronger security than security questions. If you do, then you will never have to deal with security questions again.

If you are being told there isn't enough information to reset them, contact Apple ID Support.

If you don't know the answers, if the steps in the article below don’t work, contact Apple ID Support, although I’m not sure they will be able to help. 

Apple ID - If you forgot the answers to your Apple ID security questions.      

From the article below. 

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. These policies are audited and reviewed on a regular basis.

Security and your Apple ID.    

Apple ID - Official Apple Support.    

Contact Apple for help with Apple ID account security - Apple Support.   (Link doesn't always load)  

Get Support    Work through the screens to get a chat option. 

Apple Support schedule phone call

https://twitter.com/AppleSupport