Yes. When you submit an order and you decided that you want to make changes or doesn't want to proceed you can always cancel your order. You need to got to your MARKET page, then scroll down at the bottom of the page and look for My Open Orders box. There's an option to cancel as specific order. Just click CANCEL
However, once the order has been completely matched, it will disappear from My Open Orders box and will be recorded in your Transaction History. It means that the transaction is completed. Therefore, you CANNOT cancel your order anymore.
*** If you successfully cancelled your order, you funds will will be returned to your account.