Order netoff from bracket open order


Does anyone know if its possible to reduce the size on a open order (bracket) which the bracket order will automatically netoff? Currently if i say open 2 contract with bracket order with Stop Loss and Take Profit, if it goes to my favor and i close 1 contact (with bracket off) the bracket order TP/SL will still execute with original 2 contract. How will i be able to have it taken into account? thanks