javascipt range validation for textbox inside gridview

Question

javascipt range validation(in between 0 to 50) for textbox inside gridview

here is my textbox:
<asp:TextBox ID="txtseats" runat="server" CssClass="text100" "
                                                    MaxLength="3" 
                                                    Text='<%#Eval("Nseats") %>' Height="15px" Width="39px" onclick="change()"></asp:TextBox>

i have to write this validation in button click
here is my button Control:

<asp:ImageButton ID="btnSubmit" runat="server" ImageUrl="~/Images/submit.jpg" OnClick="btnSubmit_Click"

                   Visible="False" />

i have four columns in gridview and this textbox is at fourth column