APNS token on ios update

When device was running ios 6, it had one token and I stored it in my database, then device was updated to ios 7 and got a new token. Now I have in my database 2 tokens, from ios 6 and from ios 7. Are they both valid ? Will APNS disable previous token for ios 6 ? If I send push notification using these two tokens, will the user receive duplicated messages ? How can I handle this situation ?