How to connect a stteper shield to an arduino uno if I have a 24V stepper...???

Hello... I need help and I expect that you can help me... Firstable, I usually do not write in english so, my apologies... I have and itead studio stepper shield that its suposed to be mounted in an arduino uno, but the stepper is 24V and the arduino can't reach this voltage. I tried to connect only the shield using an external source(12VDC in power jack of the shield) and the arduino across de USB port but the shield but the shield doesn't turn on... could I connect the shield to the arduino by the pins they have...??? and a external source with 12VDC...???