Rewrite your new MySqlCommand to this:
MySqlCommand cmd = new MySqlCommand("UPDATE users SET education=@c,about=@d,interest=@e WHERE user_name=@userName", con);
cmd.Parameters.AddWithValue("@c", TextBox1.Text);
cmd.Parameters.AddWithValue("@d", TextBox2.Text);
cmd.Parameters.AddWithValue("@e", TextBox3.Text);
cmd.Parameters.AddWithValue("@userName", Session["user"].ToString());
cmd.ExecuteNonQuery();
Label5.Text = "Well done profile updated!!";