Find and replace ' with ' and then " with " -- that should do the trick. I have to do that from time to time to convert straight quote marks to curlies (after I've pasted from other documents). Should work the other way around, too.That's smartquotes turned on. The answers you've been given should fix them. Or turn them off in Word. Under Autocorrect.
But I don't think turning them off will undo the ones you already have.