Yes, if you want to settle a part of your open position, you can specify the amount by the following;
1. Double-click on the position you want to manage in the "Trading" tab in the "Terminal" window
2. On the order window, make sure the order type is "Market order" and specify the volume you want to close in "Volume" field. Double check the message in yellow box "Close #OrderID side volume pair by Market" and click on it.
in the below example, volume = 1 lot out of original 3 lots of Buy UK100 will be closed and 2 lots will be remained open.
