In need of immediate help!

[rayb20]

I cannot figure out what I am supposed to increment in my aHistogram class since it is a vector itself through inheritance, this is the only thing I cannot figure out, I have completed the rest of the project successfully I just cannot figure this one part out. Any assistance would be great, since it is due in an hour :(

#ifndef AHISTOGRAM_H
#define AHISTOGRAM_H
#include <iostream>
#include <vector>
using namespace std;

class aHistogram : public aDie
{
public:
	aHistogram(); // default constructor
	void update(int face); // update histogram counts
	void display(int maxLengthOfLine); // displays histogram
	void clear(); // clears counts
	vector<int> graph;
	
private:
	int i;
	int face;
	int maxLengthOfLine;
};
#endif 

  #include <iostream>
#include <cstdlib>
#include <ctime>
#include <vector>
#include "aDie.h"
#include "aHistogram.h"
using namespace std;

aHistogram::aHistogram() // default constructor
{
	face = ((rand() % 6) + 1);
	maxLengthOfLine = 60;
	graph.resize(6);
}
void aHistogram::update(int face) // updates roll count
{
	this-> ; //NEED HELP HERE
}

void aHistogram::display(int maxLengthOfLine) // displays results
{
	int i;
	
	cout << "Face Appearances" << endl; // displays the appearances of each face
	cout << endl;
	for (i = 0; i < graph.size(); ++i)
	{
		cout << i + 1 << "---" << graph.at(i) << endl;
	}
	cout << endl;

	cout << "Histogram" << endl; // displays the histogram count
	cout << endl;
	for (i = 0; i < graph.size(); ++i)
	{
		cout << i + 1 << " - ";
		while (graph.at(i) > maxLengthOfLine)
		{
			cout << "X";
			graph.at(i) -= maxLengthOfLine;
		}
		cout << endl;
	}
	
}

void aHistogram::clear() // clears the counts for the appearances of each face 
{
	face = 0;
	maxLengthOfLine = 0;

}

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <vector>
#include "aDie.h"
#include "aHistogram.h"
using namespace std;

int main()
{
	int i;
	srand(time(0)); // seeding RNG
	
	aDie* Die1;
	aHistogram* Die2;
	vector<aDie*> DiceRoll(12000);

	Die1 = new aDie;
	Die2 = new aHistogram;

	for (i = 0; i < DiceRoll.size(); ++i) //rolls die and updates 12000 times
	{
		Die2->Roll();
		Die2->update(6);
	}
	
	Die2->display(60);

	cin.ignore();

	return 0;
}