Not like that! Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Use Parametrized queries instead.
You want something along the lines of:
using (SqlConnection con = new SqlConnection(strConnect))
{
con.Open();
using (SqlCommand com = new SqlCommand("UPDATE myTable SET myColumn1=@C1, myColumn2=@C2 WHERE RowId=@ID", con))
{
com.Parameters.AddWithValue("@ID", id);
com.Parameters.AddWithValue("@C1", myTextBox.Text);
com.Parameters.AddWithValue("@C2", myDateTimePicker.Value);
com.ExecuteNonQuery();
}
}