To modify existing records, use UPDATE statements.

Update Syntax

The UPDATE statement takes as input a comma-separated list of columns and new column values as name-value pairs in the SET clause, as shown in the following example:

UPDATE <table_name> SET { <column_reference> = <expression> } [ , ... ] WHERE { Id = <expression>  } [ { AND | OR } ... ] 

<expression> ::=
  | @ <parameter> 
  | ?
  | <literal>

You can use the ExecuteNonQuery method to execute data manipulation commands and retrieve the rows affected, as shown in the following example:

C#

String connectionString = "User=myuseraccount;Password=mypassword;URL=https://myOrg.crm.dynamics.com/;CRM Version=CRM Online;";
using (DynamicsCRMConnection connection = new DynamicsCRMConnection(connectionString)) {
  int rowsAffected;
  DynamicsCRMCommand cmd = new DynamicsCRMCommand("UPDATE Lead SET FirstName='John' WHERE Id = @myId", connection);
  cmd.Parameters.Add(new DynamicsCRMParameter("myId","1045625d-99ee-e011-a272-00155d01ad6b"));
  rowsAffected = cmd.ExecuteNonQuery();
}

VB.NET

Dim connectionString As [String] = "User=myuseraccount;Password=mypassword;URL=https://myOrg.crm.dynamics.com/;CRM Version=CRM Online;"
Using connection As New DynamicsCRMConnection(connectionString)
  Dim rowsAffected As Integer
  Dim cmd As New DynamicsCRMCommand("UPDATE Lead SET FirstName='John' WHERE Id = @myId", connection)
  cmd.Parameters.Add(New DynamicsCRMParameter("myId", "1045625d-99ee-e011-a272-00155d01ad6b"))
  rowsAffected = cmd.ExecuteNonQuery()
End Using