Could you? yes, probably, but it would be so expensive and difficult it probably wouldn't be worth it.

First the ISS doesn't have a lot of living space, probably too cramped for a long mission. Second it has no radiation shielding, which would be big, heavy and expensive to retrofit. Third, it's old and you should probably repair and upgrade it before sending it to Mars. Fourth, it would need a new engine and massive fuel tank. Fifth, it doesn't have enough electricity production for deep space, so it would need more solar panels or a nuclear reactor. Sixth, its in the wrong orbit, it's or it was picked to make it easier for Russia and Japan to send payloads to it, it's very inclined. (I think, I'm not so great at orbital mechanics.)