how do i change my security questions to verify my account when i forgot them

ssooooo recently my ipod 4 generation broke because me and my dad where trying to replace the screen and i tolled him why not get the new one that just came out. so we did nd it workes great. one problem is when i try to download and app worth money it says i have to verify on the new divise but i forgot the secrity questions how do i take them of or change them