if my laptop has two network adapters, how do I switch to one?

I suspect that the wireless adapter in this laptop is failing, because it's continually having trouble connecting, while my other laptop has none. No problem, I have a USB wireless-N adapter around somewhere. But if I plug it in, what would I have to do to make sure my laptop is using it instead of the internal wireless adapter? I guess I can always open the computer up and pull the card out, thus leaving the computer only one choice; but can't I make the system choose one or the other?