There are two options of how to cancel your order on HitBTC website.
On the main page scroll down to "My Orders and Trades" section. First tab is "Active orders" tab, where you can find "Cancel" buttons on the right side of each order. To see your active orders on all markets, click trading pair name in the header of section (for example, BTC/ETH).
Another option to cancel an order is to proceed to Reports page, "My Orders" tab. There you can filter active orders and push "Cancel" button on the right of the order you wish to cancel.