How can I change my security question and answer that i entered while registering?

I checked under Yahoo help. it was written that you log into your account and then go to options on left hand side and then on right side click on my user info but first thing, options was on right side. i clicked on that but there was no heading as My User Info. I want to know the answer ASAP if possible please because I am afraid somebody knows the answer to my security question. Please do not share this info with anyone.How can I change my security question and answer that i entered while registering?
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