Updating a Vertex Array Tile Map?

Question

I m trying to learn creating tilemap with vertex array. I found a code from a tutorial and i read its necessary to use vertex array for creating huge tilemaps if we need optimal rendering performance in a game.

class TileMap : public sf::Drawable, public sf::Transformable
{
public:

    bool load(const std::string& tileset, sf::Vector2u tileSize, const int* tiles, unsigned int width, unsigned int height)
    {
        // load the tileset texture
        if (!m_tileset.loadFromFile(tileset))
            return false;

        // resize the vertex array to fit the level size
        m_vertices.setPrimitiveType(sf::Quads);
        m_vertices.resize(width * height * 4);

        // populate the vertex array, with one quad per tile
        for (unsigned int i = 0; i < width; ++i)
            for (unsigned int j = 0; j < height; ++j)
            {
                // get the current tile number
                int tileNumber = tiles[i + j * width];
                // find its position in the tileset texture
                int tu = tileNumber % (m_tileset.getSize().x / tileSize.x);
                int tv = tileNumber / (m_tileset.getSize().x / tileSize.x);
                // get a pointer to the current tile's quad
                sf::Vertex* quad = &m_vertices[(i + j * width) * 4];

                // define its 4 corners
                quad[0].position = sf::Vector2f(i * tileSize.x, j * tileSize.y);
                quad[1].position = sf::Vector2f((i + 1) * tileSize.x, j * tileSize.y);
                quad[2].position = sf::Vector2f((i + 1) * tileSize.x, (j + 1) * tileSize.y);
                quad[3].position = sf::Vector2f(i * tileSize.x, (j + 1) * tileSize.y);

                // define its 4 texture coordinates
                quad[0].texCoords = sf::Vector2f(tu * tileSize.x, tv * tileSize.y);
                quad[1].texCoords = sf::Vector2f((tu + 1) * tileSize.x, tv * tileSize.y);
                quad[2].texCoords = sf::Vector2f((tu + 1) * tileSize.x, (tv + 1) * tileSize.y);
                quad[3].texCoords = sf::Vector2f(tu * tileSize.x, (tv + 1) * tileSize.y);

                quad[0].color = sf::Color(shadow, shadow, shadow, 255);
                quad[1].color = sf::Color(shadow, shadow, shadow, 255);
                quad[2].color = sf::Color(shadow, shadow, shadow, 255);
                quad[3].color = sf::Color(shadow, shadow, shadow, 255);
            }
        return true;
    }

private:
    virtual void draw(sf::RenderTarget& target, sf::RenderStates states) const
    {
        // apply the transform
        states.transform *= getTransform();
        // apply the tileset texture
        states.texture = &m_tileset;
        // draw the vertex array
        target.draw(m_vertices, states);        
    }
    sf::VertexArray m_vertices;
    sf::Texture m_tileset;
};

int main()
{

    // create the tilemap from the level definition
    TileMap tilemap;
    if (!tilemap.load("tilemap.png", sf::Vector2u(100, 100), level, 100, 100))
        return -1;

    //drawing tilemap
    window.draw(tilemap);


}

My question is how could i update only 1 tile or all tiles? For exaple i will detext collision between tiles and player characters. Or i would like to change tile colors etc.

Can someone explain with a minimal example code? maybe i can try to learn this subject with you help. Thanks for all answers.