Cancellations and Refunds
All fees and charges paid by you in relation to the Service are nonrefundable, except as required by law or as otherwise stated herein. You may contact Apple for a full refund within 15 days of an initial upgrade purchase or within 45 days of a subsequent yearly payment. To request a refund as described herein go to www.apple.com/support/icloud for more details. Applicable local law may vary this policy. Please contact iCloud Support for details.
You can cancel your subscription by downgrading your storage to the free 5GB plan under Storage Plan in your iCloud Account Information on your device, from your iCloud Account view in System preferences on your Mac, or from your iCloud Account view in the iCloud Control Panel for Windows on your PC. Your paid subscription will be cancelled on your next annual billing date. Partial refunds are available where required by law.
Take a look at the full iCloud Terms and Conditions.