<asp:DataList ID="Dlitems" runat="server" RepeatDirection="Horizontal" RepeatColumns="4"
                        CellPadding="0" CellSpacing="15" OnItemCommand="Dlitems_ItemCommand">
                        <HeaderTemplate>
                              <asp:Label ID="lblcat" runat="server" Text="" />
                        </HeaderTemplate>

<asp:DataList ID="Dlitems" runat="server" RepeatDirection="Horizontal" RepeatColumns="4"
CellPadding="0" CellSpacing="15" OnItemCommand="Dlitems_ItemCommand"
OnItemDataBound="Dlitems_ItemDataBound">
...

protected void Dlitems_ItemDataBound(Object sender, DataListItemEventArgs e)
{
   if (e.Item.ItemType == ListItemType.Header)
   {
       Label lblCat = (Label)e.Item.FindControl("lblcat");
       lblCat.Text = "Changed!";

    }
}

protected void dlData_ItemDataBound(object sender, DataListItemEventArgs e)
        {

    try
    {
        if (Page.IsPostBack)
        {

            if (e.Item.ItemType == ListItemType.Header)
            {
                Label lblCat = (Label)e.Item.FindControl("lblcat");
                lblCat.Text = "Changed!";


            }
        }


    }
    catch (Exception ex)
    {

        throw;
    }
   }