Saturday or Sunday? Which day is actually the 7th day, the Sabbath?

Isn't Saturday actually the day we are supposed to observe as the Sabbath? I have read that the Church changed it to Sunday to incorporate pagan worshippers into the Catholic services centuries ago. Is this true? If it is why are we still using Sunday, because it would be against Gods law, would it not? I just love the way that mankind changes Gods divine laws to please their schedules.