Resetting Security Questions

Whenever I try to buy something that costs money in the app/itunes store it always asks me for my apple security questions... I totaly forgot my answers to them and never written them down 😟 Ive been looking online for solutions and they kept saying that u could just press on the side note where u answer ur security questions that says if u want to change them, but its never there... Please help!! I need new music and app's haha