if (txtNewPassword.Text == txtConfirmPassword.Text)
{
    mSQL = "SELECT * FROM User WHERE userName = '" + txtUserName.Text + "' AND password = '" + txtPassword.Text + "'";
    mDT_Save = mDBHelper.GetTable(mSQL);
    if (mDT_Save.Rows.Count > 0)
    {
        for (int i = 0; i < mDT_Save.Rows.Count; i++)
        {
            mSQL = "UPDATE TableName SET password = '" + txtConfirmPassword.Text + "' WHERE user_name = '" + Convert.ToString(mDT_Save.Rows[i]["userName"]) + "'";
            mDBHelper.ExecuteSQLNonQuery(mSQL);
        }
        MessageBox.Show("Password Changed Successfully");
        txtPassword.Text = txtConfirmPassword.Text;
        return;
   }
   else
   {
        MessageBox.Show("User Not Found");
        return;
   }
}