I've tried to make an update statement that will update some information in my database table

protected void Page_Load(object sender, EventArgs e)
{
    FirstNameEdit.Text = Session["FirstName"].ToString();
    LastNameEdit.Text = Session["LastName"].ToString();
}
protected void SubmitEdit_Click(object sender, EventArgs e)
{
    if (FirstNameEdit.Text == "")
    {
        StatusMessage.Text = "Indtast venligst dit fornavn. ";
    }
    else
    {
        if (LastNameEdit.Text == "")
        {
            StatusMessage.Text = "Indtast venligst dit efternavn. ";
        }
        else
        {
            try
            {
                SqlConnection connection = new SqlConnection("Data Source=localhost;Initial Catalog=Break;Integrated Security=True");
                SqlCommand command = new SqlCommand("SELECT * FROM Users", connection);
                command.Connection.Open();

                string querystr = "UPDATE Users SET User_FirstName='@User_FirstName', User_LastName='@User_LastName' WHERE User_ID='@User_ID'";
                SqlCommand query = new SqlCommand(querystr, connection);

                string User_ID = Session["ID"].ToString();
                string User_FirstName = FirstNameEdit.Text;
                string User_LastName = LastNameEdit.Text;

                query.Parameters.Add("@User_ID", User_ID);
                query.Parameters.Add("@User_FirstName", User_FirstName);
                query.Parameters.Add("@User_LastName", User_LastName);
                query.ExecuteNonQuery();

                string FirstName = FirstNameEdit.Text;
                Session.Add("FirstName", FirstName);
                string LastName = LastNameEdit.Text;
                Session.Add("LastName", LastName);

                StatusMessage.Text = "Din profil er opdateret";

                command.Connection.Close();
            }
            catch
            {
                StatusMessage.Text = "Noget er galt, prøv lidt senere";
            }
        }
    }
}

I have also searched alot, but it's exactly the same I find. Maybe it's something about the SQL query.

I've tried to write an update statement that will update some information in my SQL Server table

protected void Page_Load(object sender, EventArgs e)
{
    FirstNameEdit.Text = Session["FirstName"].ToString();
    LastNameEdit.Text = Session["LastName"].ToString();
} 

protected void SubmitEdit_Click(object sender, EventArgs e)
{
    if (FirstNameEdit.Text == "")
    {
        StatusMessage.Text = "Indtast venligst dit fornavn. ";
    }
    else
    {
        if (LastNameEdit.Text == "")
        {
            StatusMessage.Text = "Indtast venligst dit efternavn. ";
        }
        else
        {
            try
            {
                SqlConnection connection = new SqlConnection("Data Source=localhost;Initial Catalog=Break;Integrated Security=True");
                SqlCommand command = new SqlCommand("SELECT * FROM Users", connection);
                command.Connection.Open();

                string querystr = "UPDATE Users SET User_FirstName='@User_FirstName', User_LastName='@User_LastName' WHERE User_ID='@User_ID'";
                SqlCommand query = new SqlCommand(querystr, connection);

                string User_ID = Session["ID"].ToString();
                string User_FirstName = FirstNameEdit.Text;
                string User_LastName = LastNameEdit.Text;

                query.Parameters.Add("@User_ID", User_ID);
                query.Parameters.Add("@User_FirstName", User_FirstName);
                query.Parameters.Add("@User_LastName", User_LastName);
                query.ExecuteNonQuery();

                string FirstName = FirstNameEdit.Text;
                Session.Add("FirstName", FirstName);
                string LastName = LastNameEdit.Text;
                Session.Add("LastName", LastName);

                StatusMessage.Text = "Din profil er opdateret";

                command.Connection.Close();
            }
            catch
            {
                StatusMessage.Text = "Noget er galt, prøv lidt senere";
            }
        }
    }
}

I have also searched a lot, but it's exactly the same I find. Maybe it's something about the SQL query.