Log in as admin, then as guest, then as a student. As each of those users go to your user profile. There should not be a link to delete your account. Directly navigate to /user/delete.php and you should get an error. As admin go to site admin > users > permissions > define roles and click the cog icon next to authenticated user. Allow moodle/user:deleteaccount. As admin and guest you still should not get a delete account link. As a student go to your own profile. You should now have a delete account link. Clicking it takes you to a confirmation screen. Clicking no should return you to your profile. Click delete my account, click yes, click continue. You should now be logged out and be unable to log back in.