The attribute points can be re-assigned freely with no charge. To do so, you need to be in town and open up your skill window. Click on the down arrow on various attributes to drop them down and in order to redistribute your attribute points.
If you have enough available unassigned attribute points, you can add those points to an attribute while in an explorable area. After the points are added, you cannot subtract points from any attribute until you return to a town or outpost. "