How to cancel an order?

To cancel an order that you have created you simply go to your application in Setting > ORDERS.

You can see different column on this page: OPEN, CLOSED, and CANCELED. You choose the order that you 

want to cancel, you put your finger on the line and slice to the left. 

A window will appear with different "reasons for the cancellation". You can pick the one which suits better and  then cancel it.