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.
Post Reviews configuration determines whether customers required to open an account with your store, purchase the product before writing product reviews or if they can submit reviews as guests. Requiring reviewers to open an account prevents anonymous, spam submissions and improves the quality of reviews.
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