After you placed some orders (market or pending) you can change some settings for them. For market orders you can change only stop loss and take profit levels, for pending orders you can also change the price. Also you can modify trailing stop parameters for both types of orders. First you should select an order in Open Positions or Pending Orders list:

Then, you can use the Modify order button on the tool bar (F4):

or click with the right mouse button on order and use this drop-down menu:

or a double click with the mouse on the order, in this case the chart will be moved to that time, when the order is placed, this time will be highlighted with a vertical line and a modify dialog will be opened. This is the dialog for a market order, with this dialog you can modify parameters (the parameters that you can not modify will be grayed) and also you can close this position:

This dialog is for a pending order, with this dialog you can modify parameters or delete a pending order:

Also you can use the tool bar buttons, hot keys or drop-down menu to close the position or delete pending orders.