You can roll over your open position by clicking on the column "Instr R/O" in your "Open Trades" window then selecting "Yes/No". 

Roll-over:

NB: You need to make sure to select instrument roll-over in order to avoid having your position closed at the expiry price. Alternatively, you can contact our trading desk for assistance. 

Your open Sep08 positions will be closed out during the GT spread, hence realising your profit or loss on that position. 

Your Dec08 positions will then be executed at the GT Bid/Offer, depending on the nature of the trade (either Bid/Offer)

Note: Should your rollover result in realizing a loss on that position, you will be required to replace the lost margin (the loss incurred in order to maintain the original risk). Should you not have sufficient funds available to facilitate this process, your risk will be reduced to a level that you will be able to fund. 

The Stop Loss in place for the trade in the expiring contract will be defaulted to an auto stop level (this may result in an additional margin requirement). The Take Profit levels will need to be re-entered when the position has been rolled into a new contract.