To make updates, you must have "Full Access" or "Limited Access - Website" permissions.
Go to the registration page where the question you want to hide is located, and click on Edit Mode.
On the top-right of the question, click the gray gear button.
Scroll down to the bottom of the question and click Show Advanced Options.
Under Advanced Options, check the box next to Hidden Question?
Click Save Question.
Hidden questions will only show for admins and not registrants.