Q: how do i change my security questions when i do not know the anwser to it

call apple care

800 692 7753 and talk to account security.

they'll help you reset if they can verify your identity i think

Forgotten Security Questions / Answers...

See Here > Apple ID: Contacting Apple for help with Apple ID account security

          Ask to speak with the Account Security Team...

Or Email Here  >  Apple  Support  iTunes Store  Contact

More Info >  Apple ID: All about Apple ID security questions

Note:

You can only set up and/or change a Rescue Email Before you forget the questions/answers.