After you placed some orders (market or pending orders) you can change some setting for them. For market orders you can change only stop loss and take profit levels, for pending orders you can also change 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 Modify order button on tool bar (F4):

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

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

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

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