In addition to the information in the knowledge base article you reference, contact Apple support at the appropriate number from http://support.apple.com/kb/HE57 and ask to speak with account security staff who can then help do the change.
If you know their current answers then you can log into your account and change them :
- Navigate to appleid.apple.com using your web browser.
- Click "Manage your account"
- When prompted, sign in using your Apple ID and password.
- Click Password & Security
- You'll be asked to answer 2 of your 3 security questions before you can make any modifications. If you are unable to remember your answers, you can choose to send an email to your rescue email to reset your security questions.
- After you've validated your identity by correctly answering your security questions, click Edit to the right of your rescue email address.
- Once you've finished editing your rescue email address, click the Save button directly below the email field.
If you can't remember their answers and you have a rescue email address (which is not the same thing as an alternate email address) set up on your account then you can go to https://appleid.apple.com/ and click 'Manage your Apple ID' on the right-hand side of that page and log into your account. Then click on 'Password and Security' on the left-hand side of that page and on the right-hand side you might see an option to send security question reset info to your rescue email address.
If you don't have a rescue email address (you won't be able to add one until you can answer 2 of your questions) then see if this user tip helps : https://discussions.apple.com/docs/DOC-4551
e.g. you can try contacting iTunes Support : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Account Management , and then try Apple ID Account Security
or try ringing Apple in your country and ask to talk to the Accounts Security Team : http://support.apple.com/kb/HE57