The "security question" section of the Google Account settings page informs users that "We no longer support security questions as a way to access your account. Please consider adding a recovery phone or recovery email address to keep your account secure." You can only delete your security question.
Security questions weren't a great way to protect an account since many answers could be guessed or found using a Google search. For example, Sarah Palin had her Yahoo email account compromised by someone who found the answers to her secret questions. "The hacker simply reset Palin's password using her birthdate, ZIP code and information about where she met her spouse — the security question on her Yahoo account, which was answered (Wasilla High) by a simple Google search."