Users can cancel their Orders which is not executed.

The orders can get cancelled from Dashboard or Spot Exchange 

In the Dashboard page Open order section do cancel the orders.

Open Orders in Dashboard:

Suppose if you want to cancel the all open orders select Cancel All.

After confirming, all orders will be cancelled. 

The order cancellation also is done from Spot Exchange My Open Order section.

Open Orders in Spot Exchange

Hope this answer helps.