
Canceling an order is the usual way to remove an order from the market, if it has been sent but not filled. The Cancel Order page sends a normal cancellation to the ECN.
(For stuck orders, Nuke Order.)

Click the Cancel Order link under the Trades or Server Data tab.
Specify a Server in the field provided. (Example: EXEC)
Type the Order Number you wish to cancel in the field provided (Example: 999999)