Functional VBO Modification C# OpenTK

using OpenTK;
using OpenTK.Graphics;
using OpenTK.Graphics.OpenGL;
using OpenTK.Input;
using System;

namespace OpenTKTest
{
    internal class Window : GameWindow
    {
        float[] vertices = {
            -0.5f, -0.5f, 0.0f, //Bottom-left vertex
            0.5f, -0.5f, 0.0f, //Bottom-right vertex
            0.0f,  0.5f, 0.0f  //Top vertex
        };

        int VertexBufferObject;
        int VertexArrayObject;

        Shader shader;

        public Window(int width, int height, string title)
            : base(width, height, GraphicsMode.Default, title)
        {

        }

        protected override void OnLoad(EventArgs e)
        {
            GL.ClearColor(1.0f, 0.0f, 1.0f, 1.0f);

            shader = new Shader("..\\..\\vertex.vert", "..\\..\\fragment.frag");

            VertexBufferObject = GL.GenBuffer();

            // INITIAL DRAW - NO SUB
            GL.BindBuffer(BufferTarget.ArrayBuffer, VertexBufferObject);
            GL.BufferData(BufferTarget.ArrayBuffer, vertices.Length * sizeof(float), vertices, BufferUsageHint.DynamicDraw);

            GL.VertexAttribPointer(shader.GetAttribLocation("aPosition"), 3, VertexAttribPointerType.Float, false, 3 * sizeof(float), 0);
            GL.EnableVertexAttribArray(0);

            // DRAW EVERY RENDER
            VertexArrayObject = GL.GenVertexArray();
            GL.BindVertexArray(VertexArrayObject);

            GL.BindBuffer(BufferTarget.ArrayBuffer, VertexBufferObject);
            GL.BufferSubData(BufferTarget.ArrayBuffer, (IntPtr)(0), vertices.Length * sizeof(float), vertices);
            //GL.BufferData(BufferTarget.ArrayBuffer, vertices.Length * sizeof(float), vertices, BufferUsageHint.StaticDraw);

            GL.VertexAttribPointer(shader.GetAttribLocation("aPosition"), 3, VertexAttribPointerType.Float, false, 3 * sizeof(float), 0);
            GL.EnableVertexAttribArray(0);

            base.OnLoad(e);
        }

        protected override void OnRenderFrame(FrameEventArgs e)
        {
            GL.Clear(ClearBufferMask.ColorBufferBit);

            vertices[3] = 0.2f;

            /**
            shader.Use();
            GL.BindVertexArray(VertexArrayObject);
            GL.DrawArrays(PrimitiveType.Triangles, 0, 3);
            **/

            shader.Use();

            GL.BindBuffer(BufferTarget.ArrayBuffer, VertexBufferObject);
            GL.BufferSubData(BufferTarget.ArrayBuffer, (IntPtr)(0), vertices.Length * sizeof(float), vertices);
            //GL.BufferData(BufferTarget.ArrayBuffer, vertices.Length * sizeof(float), vertices, BufferUsageHint.StaticDraw);

            GL.VertexAttribPointer(shader.GetAttribLocation("aPosition"), 3, VertexAttribPointerType.Float, false, 3 * sizeof(float), 0);
            GL.EnableVertexAttribArray(0);

            GL.DrawArrays(PrimitiveType.Triangles, 0, 3);

            Context.SwapBuffers();
            base.OnRenderFrame(e);
        }

        protected override void OnUpdateFrame(FrameEventArgs e)
        {
            var input = Keyboard.GetState();

            if (input.IsKeyDown(Key.Escape))
            {
                Exit();
            }

            base.OnUpdateFrame(e);
        }

        protected override void OnResize(EventArgs e)
        {
            GL.Viewport(0, 0, Width, Height);
            base.OnResize(e);
        }

        protected override void OnUnload(EventArgs e)
        {
            GL.BindBuffer(BufferTarget.ArrayBuffer, 0);
            GL.DeleteBuffer(VertexBufferObject);

            shader.Dispose();

            base.OnUnload(e);
        }
    }
}