Q: How do you change your security questions when you forgot them

Hello, Zhang Johan. 

Thank you for visiting Apple Support Communities.

If you need to reset your security questions and have a rescue email attached to your Apple ID, this article will help you with this issue.

Rescue email address and how to reset Apple ID security questions

http://support.apple.com/kb/HT5312

If you are still unable to reset your security questions or do not have a rescue email associated with your account, you will need to reach out to our account security team.

Apple ID: Contacting Apple for help with Apple ID account security

http://support.apple.com/kb/HT5699

Cheers,

Jason H.