Forms Data Controls :: Change Values Associated With Labels

I have a gridview and there is a templateField with a few labels in it. I have a dropdownlist in a headertemplate and when the selectedindexchanged event I am trying to change the values associated with those labels. The name of the gridview is Gridview1. Here is the template field when it is first shown

<asp:TemplateField ItemStyle-CssClass="phoneCostsPhoneStyle" >
<ItemTemplate>
<div style="position:relative">
<asp:Label ID="lblDayCallPhone" runat="server" Text="Day:" CssClass="lblDayCallPhoneStyle"></asp:Label>
<asp:Label ID="lblDayCostsPhone" runat="server" Text='<%# Eval("NATIONAL_DAY", "{0:C}") %>' CssClass="lblDayCostsPhoneStyle"></asp:Label><br /><br />
<asp:Label ID="lblEveningCallPhone" runat="server" Text="Evening:" CssClass="lblEveningCallPhoneStyle"></asp:Label>
<asp:Label ID="lblEveningCostPhone" runat="server" Text='<%# Eval("NATIONAL_EVENING", "{0:C}") %>' CssClass="lblEveningCostPhoneStyle"></asp:Label><br /><br />
<asp:Label ID="lblWeekendCallPhone" runat="server" Text="Weekend:" CssClass="lblWeekendCallPhoneStyle"></asp:Label>
<asp:Label ID="lblWeekendCostPhone" runat="server" Text='<%# Eval("NATIONAL_WEEKEND", "{0:C}") %>' CssClass="lblWeekendCostPhoneStyle">.........