If you need to cancel a Share use Share Management → Details for the Share. “Cancel” is the first option. This will cancel delivery for all files included in the Share. You can’t “reactivate” a cancelled Share.

If you used the “Send File(s) using My Docs Online” option there will be a separate Share for each email address and each one must be cancelled individually.

The details page for the Share also includes the link, which can be copied to send again in your own email message.

To change the expiration of a Share (to expire it sooner or later than originally set) use “change expiration”. You can’t extend expiration after the Share has already expired.