This will set the page of the table to the first one
public void changeMethod() {
final DataTable d = (DataTable) FacesContext.getCurrentInstance().getViewRoot()
.findComponent("myDataTable");
int first = 0;
d.setFirst(first);
}
Or on client side:
widgetVar.getPaginator().setPage(pageindex);
EDIT : The "first" attribute indicates the index of the first row to be displayed