In order to delete your Ruuvi account (Ruuvi Station app account) and associated data such as history data stored in the Ruuvi Cloud database and custom sensor settings (name, alert limits, offsets), please tap "Delete Account" button on your Ruuvi Station mobile app or web interface and follow instructions that will be emailed to you. You can find the button under "My Ruuvi Account" menu item.
If you would like to only partially delete your data, please email us at support@ruuvi.com and we assist you on the request.