How to delete a question already in use?

How to delete a question already in use?

I have entered a value to a question I now want to remove.
 
It is saying can't be deleted and in use by a user.
 
I am the only user and how can I remove the value from this question.
 
I only want 3X secuirty questions and there is currently 4X which is confusing to users.
 
Thanks,
Liam

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