Close a third of the position

Hi,

I was wondering if someone was able to explain how I could partially close the trade please?

So for example if I have a trade and I am risking 3% of my account balance, when the trades get to 2% profit I want to close 1% (I guess 33% of the trade volume) of that trade and then leave the other 2% (66% of the trade) open.

Cheers,

Jay

this is my current code that doesnt seem to work:

                        double currentVolume = position.VolumeInUnits;
                        double newVolume = currentVolume * 0.66;

                        if (position.ModifyVolume(newVolume).IsSuccessful)
                        {

                                //trade partially closed - but this never seems to get here

                         }