The HT5312 page that you posted from has instructions for how to reset them i.e. if you have a rescue email address (which is not the same thing as an alternate email address) on your account then steps 1 to 5 half-way down that page should give you a reset link.
If you don't have a rescue email address (you won't be able to add one until you can answer your questions) then you will need to contact Support in your country to get the questions reset (these are user-to-user forums).
Contacting Apple about account security : http://support.apple.com/kb/HT5699
When they've been reset (and if you don't already have a rescue email address) you can then use the steps half-way down the HT5312 page that you posted from to add a rescue email address for potential future use