Once you have applied for a job, your answers to qualification questions are saved in your profile to save you time on subsequent applications. If you would like to change what these answers are, click on the User Profile button in the top right and go to the Job Default Answers tab:
There, you can view the answers that have been saved.
If you would like to change your default answers, simply click on the "X" to the right of the answer to remove it. You will then be asked this question on your next job application.