After you’ve unlocked your wallet, click on “My Activity” →“Active Orders” in the top navigation. This will take you to a dedicated page for open orders.
On this page you can see all of your open orders and cancel them individually.
If you are using a keystore/private key wallet, the orders are cancelled immediately. If you are using MetaMask or Ledger wallet then you have to sign the message and approve the cancellation.
Users can also view and cancel open orders on the trading page of each market. The open orders are found in the “Active Orders” table below the price chart.