ok, if its early, its simple unscrew it from the thermostat housing, but warm the engine first *
if its a late, there is a "R" clip that holds it into the housing, and a rubber "O" ring that seals it. you will prob find its stuck in place even after you take the "R" clip out, be gentle, and dont break the housing..
*warm, not hot, just so the thermostat housing is warm to the touch, any hotter then you could burn yourself as the coolant comes out
it would have helped if you had told us what year the van is.
just be aware that you will be getting a arm and pit full of coolant when you take that sensor out on a late cooling system, its a 17mm hole you are unplugging.....