If you have signed up to SwiftKey Cloud, then you can remove your account and all data attached to your account in the following way:
- Open the SwiftKey app from the list of apps on the device
- Tap ‘My Profile'
- Tap on your account
- Press ‘Delete account’ and then ‘delete’ on the pop up screen
You can also simply log out of your Cloud Account, which will stop sending any further Cloud data to the SwiftKey servers.
If you haven't signed up to SwiftKey Cloud, for instructions on how to remove the personal language data stored on your device please see this article, 'How do I clear data stored on my device?'.