If you place a limit order on the order book it will stay until it fills or expires. If you would like to cancel the order early here is how you do so.
Click on the little green wallet next to your order.
This will bring up your order in the order handler and the option to cancel.
This will bring up the gas handler if you are using Ledger or the Metamask confirmation.
Be aware that cancelling an open order will cost gas because it is sending the cancellation to the blockchain.
To see information about what costs gas see the article When Do I Pay Gas?