👋 Hi @Kenji Naito, welcome to the Box Community! I understand you’d like to change your plan.
To assist you, please email cancel@box.com using your admin email and include your request. Kindly specify the plan you'd like to downgrade to, along with your preferred billing frequency (monthly or annual, if applicable). Our specialists will review your account and proceed with your request in accordance with Box's terms, and will follow up with you via email.
You can check this article for reference: Downgrading Your Box Account
If you have any other concerns, feel free to let us know. 😊