It is possible to close your position using a variety of order types.


If you previously bought or are long, submit a "Sell / Short" order with a quantity equal to the size of your position. 


If you previously sold or are short, submit a "Buy / Long" order with a quantity equal to the size of your position. 


You may also click the "Close" button, which submits a Limit order, or the "Market" button, which submits a Market order, next to your position on the Open Positions tab.