Reduce seat from four to one.

Hi Takashi, 

Welcome to the Box Community, I'm happy to help!

Have you checked out this article on how to reduce the seats for your account?: https://support.box.com/hc/en-us/articles/360044193073-Decreasing-Seats-From-Your-Subscription 

To reduce the number of purchased seats (licenses) from your subscription, have the account administrator submit a request to cancel@box.com. Include the total number of seats you would like to continue purchasing in your email. We have a minimum purchase of 3 seats per account.

Seat decreases can only be processed at the end of the account's term. If requesting to decrease seats, please ensure the number of users on the account align with your request as there cannot be any discrepancy between billing and usage. Please reach out to our cancellations team about the eligibility of your request.

All the best, 

Hi France,
Thank you for letting me know! I will contact the cancel team.