Update Specific Row?

Hi, I'm a newbie doing my very first UPDATE procedure. I want to UPDATE a specific row in my Sql db table, WHERE FirstName = "John" AND LastName = "Smith". What am I missing in my code below to do this specific update:    Most greatful for any help, thanks.<asp:SqlDataSource ID="SqlDataSource3" runat="server"

ConnectionString="<%$ ConnectionStrings:ConnectionString %>"

UpdateCommand="UPDATE [CompanyDepartment] SET [User_Name] = @User_Name, [FirstName] = @FirstName, [LastName] = @LastName, [Company_Name] = @Company_Name, [Department_Name] = @Department_Name WHERE [User_ID] = @User_ID ">

<updateparameters>

<asp:parameter Name="User_Name" Type="String" />

<asp:parameter Name="FirstName" Type="String" />

<asp:parameter Name="LastName" Type="String" />

<asp:Controlparameter Name="Company_Name" Type="String" ControlID ="ListBox1" PropertyName ="SelectedValue" />

<asp:Controlparameter Name="Department_Name" Type="String" ControlID ="ListBox2" PropertyName ="SelectedValue"/>

<asp:parameter Name="User_ID" Type="Int32" />

</updateparameters>

</asp:SqlDataSource>