When you use the UpdatePanel to implement partial updates,the scroll position will be maintained between the asynchronous post-backs.However,you may need to reset the scroll position after the partial update completed ( after receiving the response).
To do that you can handle the PageRequestManager endrequest event and use window.scrollTo JavaScript method.
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<script type="text/javascript">
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(function() { window.scrollTo(0, 0); });
</script>
Note: make sure to place the scrip inside the Form element , otherwise you will get exceptions like Sys is not defined.