C# code for change password?

protected void Button1_Click(object sender, EventArgs e)
{
 
string paswd;
paswd="NewPass" // set your password
String str = "update reg set password=@pass where u_name=@u_name and password=@oldpass ";
cmd = new SqlCommand(str, con);
cmd.Parameters.AddWithValue("oldpass",oldpass.Text);
cmd.Parameters.AddWithValue("pass",paswd);
cmd.Parameters.AddWithValue("u_name",txt_nPW.Text);
 
con.Open();
cmd.ExecuteNonQuery();
con.Close();
Response.Write("Password Changed");
 
}
 

class Userdetails
	{
            public static string username;
            public static string password;
     }
 
SqlConnection Connection = new SqlConnection("Data Source=FARZADFWADIA-PC;Initial Catalog=HRMS;Integrated Security=True");
Connection.Open();
 
if (textBox_New.Text.Length < 4)
	{
		MessageBox.Show("The Length of the password must be 			atleast in four chars.", "Update Failed"); return;
	}
 
if (textBox_New.Text != textBox_Verify.Text)
	{
		MessageBox.Show("New Password dose not match Confirm 			Password.", "Update Failed"); return;
	}
 
if (Userdetails.password != textBox_Current.Text)
	{
		MessageBox.Show("Old Password is not valid.", "Update 		Failed");
		return;
	}
 
Userdetails.password = textBox_New.Text;
SqlCommand cmd = new SqlCommand("update Login set password=@UserPassword where username="+Userdetails.username);
cmd.Parameters.AddWithValue("@UserPassword", textBox_New.Text);
 
if (cmd.ExecuteNonQuery().ToString() == "0")
	{
		MessageBox.Show("Password changed successfully.", 			"Process Completed", MessageBoxButtons.OK, 				MessageBoxIcon.Information);
	}
else
	{
		MessageBox.Show("Due to some problems your password 			cannot be changed. Contact your administrator to 			change it 	or try again later.", "Update Failed", 			MessageBoxButtons.OK,MessageBoxIcon.Warning);
	}
 
this.Close();