Go to System → Settings → General
Enable/Disable new review entry. This will change visibility or completely hide the write review form on the StoreFront product page.
Four options available:
Do not allow - the write review form will be hidden for any customer or visitor
Any customer or visitor - anyone allowed to post new product's reviews
Registered Customer - only logged-in customers allowed to post product reviews
Customer with verified order - only logged-in customers who purchase the product allowed to post purchased product's reviews
All posted reviews are moderated by the Admin Users in the Catalog → Reviews.