The Downgrading Process
Right now the easiest path to downgrade your account is to reinstall the app.
First head over to the apps page in your Shopify dashboard.
Next locate the Has It Shipped Yet App and click on the x icon (delete icon).
Now just click delete. This will remove the Has It Shipped Yet from your shop.
Once you have deleted the app, you'll need to reinstall it from the Shopify App Store (here).
Note: You'll get a couple of automated emails after the reinstallation happens, feel free to just ignore them.