If you're not already on the Free plan, you must first go through the downgrade flow to be able to cancel your account and delete all data.
Once your account has been downgraded, from the Account tab, you can click the Cancel your account hyperlink at the bottom of the page.
Canceled accounts are immediately deleted from the system along with all data.
If you have any issues canceling your account, please message us through the chat or email support@lingq.com.