There is a new way to downgrade your plan.
1) First, you want to access your account, make sure to log in to like normal > http://qbo.intuit.com.
2) Copy and paste this link (once you’re already logged in) > https://qbo.intuit.com/app/changeplan
3) It shows you choices to downgrade. Pick new “Choose plan” button. Make sure to review what features will be disabled.
4) Confirm it, and log back in.
Alternatively, you can also call support at 1-888-333-3451. Currently, the downgraded plan is available for the US customers only.
For more video tutorial, check out this short video.