use this
<Columns>
<asp:TemplateField ItemStyle-Width="90px">
<EditItemTemplate>
<asp:ImageButton ID="imgbtnUpdate" CommandName="Update" runat="server" ImageUrl="~/Images/update.png"
ToolTip="Update" />
<asp:ImageButton ID="imgbtnCancel" runat="server" CommandName="Cancel" ImageUrl="~/Images/Cancel.png"
ToolTip="Cancel" />
</EditItemTemplate>
<ItemTemplate>
<asp:ImageButton ID="imgbtnEdit" CommandName="Edit" runat="server" ImageUrl="~/Images/Edit.png"
ToolTip="Edit" />
<asp:ImageButton ID="imgbtnDelete" CommandName="Delete" Text="Edit" runat="server"
ImageUrl="~/Images/delete.png" ToolTip="Delete" Height="20px" Width="20px" />
</ItemTemplate>
<FooterTemplate>
<asp:ImageButton ID="imgbtnAdd" runat="server" ImageUrl="~/Images/AddNewitem.png"
CommandName="AddNew" />
</FooterTemplate>
</asp:TemplateField>