The valve stems are attached to the tubes. Go and look at the valves that are on your bike now. The stems will look like one of these:
The problem will be that the valve stem holes in your rims will be larger if you have shrader valves. If you try to put a presta tube in a shrader rim the hole will be too big and you will need some type of grommet so the valve stem won't move around.
I'm guessing that you have shrader valve tubes/rims. If so, the best thing to do is cal AE and order the proper tubes.