You will need to have flight modes engaged, I have a DSx9 which I believe is the same as the Jr 9x series.

Once the flight modes are activated you will need to set mixes up so that on flight mode 3 or which ever one you want the flaps will act with the ailerons, and on the other flight modes they act as normal flaps. remember to switch back to landing flight mode before engaging flaps though otherwise you will overload the servo's

Its like 9pm here and I got work in the morning so some kind soul might give you a more detailed step by step explanation, if not I will try and write one tomorrow.