How to upate a populated checkboxlist?

I have a checkboxlist that is already populated.

Now, I'm frustrated on how to update the checkboxlist, e.g. uncheck one of the checkboxes or check one of the checkboxes.

In page.aspx:

    <asp:CheckBoxList ID="cblSW" runat="server" DataTextField="SoftwareID" DataValueField="SoftwareID" >
    </asp:CheckBoxList><br />
    <asp:Button ID="btnUpdateSW" runat="server" Text="Button" />

 In page.aspx.cs:

 ....//Populate checkboxlist

        SqlConnection con = new SqlConnection("Data Source=localhost;initial catalog=ams;user id=sa; password=sa2008");
        SqlCommand cmd = new SqlCommand("SELECT SoftwareID FROM SoftwareList order by SoftwareID ...