JavaScript Validation in the Gridview

<script src="Scripts/jquery-1.4.1-vsdoc.js" type="text/javascript"></script>
        <script type="text/javascript">
            $(document).ready(function () {
                $("#lkPaymentMethod").click(function () {

function requiredfiled() {
                var UpdatePaymentMethod = $('#txtPaymentMethod').val();
                var paymentmethod = $('#txtInsertPaymentMethod').val();
                   if (paymentmethod == "") {
                       $('#label1').html("Please Fill Payment Method");
                       return false;
                }

<asp:GridView ID="grdPaymentMethod" runat="server" AutoGenerateColumns="False" OnRowCancelingEdit="grdPaymentMethod_RowCancelingEdit"
                OnRowCommand="grdPaymentMethod_RowCommand" OnRowEditing="grdPaymentMethod_RowEditing"
                ShowFooter="True" OnRowDeleting="grdPaymentMethod_RowDeleting" OnRowUpdating="grdPaymentMethod_RowUpdating">
                <Columns>
                    <asp:TemplateField HeaderText="ID">
                        <EditItemTemplate>
                            <asp:Label ID="lbEditPaymentMethodID" runat="server" Text='<%# Eval("UserPaymentMethodID") %>'></asp:Label>
                        </EditItemTemplate>
                        <ItemTemplate>
                            <asp:Label ID="lbPaymentMethodId" runat="server" Text='<%# Eval("UserPaymentMethodID") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Payment Method">
                        <EditItemTemplate>
                            <asp:TextBox ID="txtPaymentMethod" ClientIDMode="Static"  runat="server" Text='<%# Eval("PaymentMethod") %>'></asp:TextBox>
                        </EditItemTemplate>
                        <FooterTemplate>
                            <asp:TextBox ID="txtInsertPaymentMethod" ClientIDMode="Static" runat="server"></asp:TextBox>
                        </FooterTemplate>
                        <ItemTemplate>
                            <asp:Label ID="lbPaymentMethod" runat="server" Text='<%# Eval("PaymentMethod") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField>
                        <EditItemTemplate>
                            <asp:LinkButton ID="btnUpdate" runat="server" OnClientClick="javascript:return requiredfiled();" CommandName="Update">Update</asp:LinkButton>
                            <asp:LinkButton ID="btnCancel" runat="server" CommandName="Cancel">Cancel</asp:LinkButton>
                        </EditItemTemplate>
                        <FooterTemplate>
                            <asp:Button ID="btnSave" runat="server" OnClientClick="javascript:return requiredfiled();" CommandName="Save" Text="Submit" />
                        </FooterTemplate>
                        <ItemTemplate>
                            <asp:LinkButton ID="lkEdit" runat="server" CommandName="Edit">Edit</asp:LinkButton>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField>
                        <ItemTemplate>
                            <asp:LinkButton ID="btnDelete" runat="server" CommandName="Delete">Delete</asp:LinkButton>
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>
            </asp:GridView>