Show data in texbox c #, edit and update?

This time I bring a little problem that is stinging me. It's about that I have a form of a web solution in c # with asp.net that I want to edit. The data I want to edit is a table called User made in Sql Server.

The data of a particular user I have been able to recover, I have even put in the form so that you can see what you want to change. But when I delete the text box to put a new datum and press update, it keeps the same values I had before I deleted them.

I have noticed that every time I press update the page is loaded again from the Load, which is where I recover the data. From what I see, that is the problem. I'm not very familiar with this language and that's why I've been struggling with this update section.

protected void Page_Load(object sender, EventArgs e)
    {
        idUsuario = actualizar.getId();
        Modificacion modificacion = new Modificacion();

        txtNombre.Text = modificacion.mostrarNombre(idUsuario.ToString());
        txtCorreo.Text = modificacion.mostrarCorreo(idUsuario.ToString());
        txtUsuario.Text = modificacion.mostrarUsuario(idUsuario.ToString());                

    }

The action that the update button produces is:

 protected void btnActualizar_Click(object sender, EventArgs e)
    {

        String nombre = txtNombre.Text;
        String correo = Convert.ToString(txtCorreo.Text);
        String user = Convert.ToString(txtUsuario.Text);
        String estado = listEstado.SelectedValue;


        Actualizacion actualizacion = new Actualizacion();

        if (estado.Equals("Activo"))
        {
            actualizacion.actualizarUsuario(idUsuario.ToString(), nombre, correo, user, "1");
        }
        else
        {
            actualizacion.actualizarUsuario(idUsuario.ToString(), nombre, correo, user,"2");
        }     
    }

In short, my goal is to show the user's data in the text boxes without, when I delete the data and write the new information, I continue adding the values that I found from the database. I would greatly appreciate the help of this community. Thanks.