The polarity of the sustain pedal is determined by the keyboard when it is powered up. On power up, the sustain pedal is assumed to be in the OFF position. So, if you want the sustain pedal to be off when it is unpressed, make sure the pedal is unpressed when you power up.
If the sustain pedal works "the wrong way around" although the pedal wasn't pressed on power-up, turn your Sereis II MIDI keyboard off again and then power it on while holding the sustain pedal down. This will reverse it's polarity.