The basic form is:
UPDATE MyTable SET <column name> = <new value> WHERE <ID column name> = <ID Value>
So code like this changes a single row:
using (SqlConnection con = new SqlConnection(strConnect))
{
con.Open();
using (SqlCommand com = new SqlCommand("UPDATE myTable SET myColumn1=@C1, myColumn2=@C2 WHERE Id=@ID", con))
{
com.Parameters.AddWithValue("@ID", id);
com.Parameters.AddWithValue("@C1", myValueForColumn1);
com.Parameters.AddWithValue("@C2", myValueForColumn2);
com.ExecuteNonQuery();
}
}