It is always good practice to provide 24 hours or more advanced notice of needing to cancel a meeting. There are a few ways to do so.
1) If you are the Requestor of the appointment you can send a message to the other party through the calendar list (or by searching on their name and sending a Message that way).
2) And the person who accepted the request to meet, can cancel the meeting by clicking on Decline within their scheduled calls section of Veditz. This will send a Cancelation message to the Requestor. An optional message as to why the meeting is being canceled can be included in the message.