VertexArray and FloatBuffer modification (beginner question)

Hello.
Can any one tell me how to modify FloatBuffer for example I’m keeping square in FloatBuffer now when i press some key
new square will be add to FloatBuffer and display.
Do modification FloatBuffer is possible and if so do this operation is slow?


public void gameLoop(){
		final int vertices = 8;
        final int vertexSize = 3;
        final int colorSize = 3;
		
        FloatBuffer vertexData = BufferUtils.createFloatBuffer(vertices * vertexSize);
        vertexData.put(new float[]{-0.5f,  0.5f,  0.0f,  0.5f,  0.5f,  0.0f,  0.5f, -0.5f,  0.0f, -0.5f, -0.5f,  0.0f});
        vertexData.flip();

        FloatBuffer colorData = BufferUtils.createFloatBuffer(vertices * colorSize);
        colorData.put(new float[]{1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f});
        colorData.flip();
        
		while(running) {
			update();
			glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
			glLoadIdentity();
			GL11.glTranslatef(0.0f, 0.0f, -6.0f);
			
			glEnableClientState(GL_VERTEX_ARRAY);
            glEnableClientState(GL_COLOR_ARRAY);
			
            glVertexPointer(vertexSize, 0, vertexData);
            glColorPointer(colorSize, 0, colorData);
            
            glDrawArrays(GL_QUADS, 0, vertices);
            
            glDisableClientState(GL_COLOR_ARRAY);
            glDisableClientState(GL_VERTEX_ARRAY);
			
			Display.sync(60);
			Display.update();
		}
		
		Display.destroy();
	}

Everything you need to know:
http://docs.oracle.com/javase/6/docs/api/java/nio/FloatBuffer.html

Lazy me