Yes, you can cancel a placed order by finding it in the Open orders tab present on your dashboard. The order gets canceled only when the order is in the 'Not processed' or to be 'processed statue'.
Login to your account using your UCC code and password
Go to Open Orders tab on your dashboard
From the list of orders find the order you want to modify
Click the cancel button corresponding to the order you wish to cancel
A pop up message appears on the screen with a message that the order has been canceled.