How can I change my secret question?

The directions for changing them are midway through the following article. https://support.apple.com/en-us/HT201363

-AJ

If you have not forgotten the answers to the ones you have now, then this support article will provide the steps you need:

About Apple ID security questions - Apple Support

If you have forgotten the answers, you will have to contact Apple Support to have them reset:

ACCOUNT SECURITY CONTACT

Cheers,

GB