The steps for canceling QuickBooks Online depend on where you signed up for your subscription. If you subscribe through a mobile app store, you'll need to go to Google Play or Apple App Store to close your account.
However, if you purchase your account directly from Intuit, go to Settings (Gear icon) > Subscription and billing under Profile > Cancel subscription and follow the prompts. Make sure you are logged in as either a Master Administrator or Company Administrator.
Once finished, you'll receive an email confirmation. Your access will remain in read-only mode for up to one year. After this time, your data will be permanently deactivated. I recommend exporting the report that you may need in the future.
If you have any further questions, please don't hesitate to return to this thread. We'll be here to help you.