Speak & Improve is part of the & Improve family, which includes Write & Improve. When you create a profile for Speak & Improve or Write & Improve, your profile is the same for both apps.
You can remove your account and all the personal data related to it at Write & Improve by following these instructions: https://help.writeandimprove.com/en/articles/2322280-i-want-to-cancel-my-account.