The free subscription does not expire, it just is limited for example that you can not be adding too many new words to your account (That limit will be gradually reducing until it stays at 10 per week).
If you want to delete the account, you just can use the "Feed back" button on our website and select to delete your account, or you just write us an email to cs@trainchinese.com. If the account does include many words or if the account has a paid subscription we certainly will ask for a confirmation before deleting it.