In order for a student to delete their account, they will need to get in touch with you (the site owner) to do so. We highly recommend confirming that they want to delete their account and double checking that they're contacting you from the email on file to make sure you don't delete them by accident as you will not be able to restore their account progress/details if it was deleted by accident.
Once you've confirmed they wish to completely delete their account, go into the Users section of your dashboard, and find the student. From there, on the right-hand side of the row, you'll see a button with three dots pop up which you can click to show the delete option. You should be prompted to confirm that you want to delete the account and you'll need to press "Delete User" to finalize the deletion.
If the student had any active subscriptions on their account, you'll need to cancel their subscription in Stripe manually as well - you can read more about how to do that here.