Political change never happens by voting in one political party instead of the other political party.

And that's largely true, assuming that by "political change" you mean desirable political change. But voting in one political party instead of another can certainly bring about undesirable political change, and can bring desirable political change to a shuddering halt. As witness, for a prime example, Germany in 1933. (And that doesn't mean I'm saying that Bush is a clone of Hitler - if I don't put that in, someone is bound to claim I said that.)