<asp:FormView ID="FormView1" runat="server" DataKeyNames="id" 
        DataSourceID="AccessDataSource1">
        <EditItemTemplate>

            ...

            Num:
            <asp:TextBox ID="NumTextBox" runat="server" Text='<%# Bind("Num") %>' />
            


            ...

            <asp:LinkButton ID="UpdateButton" runat="server" CausesValidation="True" 
                CommandName="Update" Text="Update" />
            &nbsp;<asp:LinkButton ID="UpdateCancelButton" runat="server" 
                CausesValidation="False" CommandName="Cancel" Text="Cancel" />
        </EditItemTemplate>
        <InsertItemTemplate>
           ...
           
           Num:
            <asp:TextBox ID="NumTextBox" runat="server" Text='<%# Bind("Num") %>' />
            


           ...          

            <asp:LinkButton ID="InsertButton" runat="server" CausesValidation="True" 
                CommandName="Insert" Text="Insert" />
            &nbsp;<asp:LinkButton ID="InsertCancelButton" runat="server" 
                CausesValidation="False" CommandName="Cancel" Text="Cancel" />
        </InsertItemTemplate>
        <ItemTemplate>

          ...

            Num:
            <asp:Label ID="NumLabel" runat="server" Text='<%# Bind("Num") %>' />
            


           ...

            <asp:LinkButton ID="EditButton" runat="server" CausesValidation="False" 
                CommandName="Edit" Text="Edit" />
            &nbsp;<asp:LinkButton ID="DeleteButton" runat="server" CausesValidation="False" 
                CommandName="Delete" Text="Delete" />
        </ItemTemplate>
    </asp:FormView>

    <asp:Button ID="Button_Edit" runat="server" onclick="ButtonEdit_Click" 
        Text="Изменить" />

&nbsp;<asp:Button ID="Button_Save" runat="server" onclick="ButtonSave_Click" 
        Text="Сохранить" />
    


    <asp:AccessDataSource ID="AccessDataSource1" runat="server" 
        DataFile="*\DB*.accdb" 
        DeleteCommand="UPDATE SchetFaktura SET Active = false WHERE id =?" 
        SelectCommand="SELECT ... Num, ... FROM Table ORDER BY addDate" 
        UpdateCommand="UPDATE Table SET Num = ? WHERE id = ? " >
        
    </asp:AccessDataSource>

 protected void ButtonEdit_Click(object sender, EventArgs e)
    {
        FormView1.ChangeMode(FormViewMode.Edit);
    }
    protected void ButtonSave_Click(object sender, EventArgs e)
    {
        FormView1.UpdateItem(true);
    }

Для обновления записи FormView 'FormView1' должно находиться в режиме правки.