<asp:GridView ID="gvFiles" runat="server" AutoGenerateColumns="False"
    OnPageIndexChanging="gvFiles_PageIndexChanging"
    OnSelectedIndexChanged="renFile" OnRowCommand="gvFiles_RowCommand"
    OnRowDataBound="gvFiles_RowDataBound" OnRowDeleting="delFile">
    <AlternatingRowStyle />
    <Columns>
        <asp:TemplateField HeaderText="Name" SortExpression="Name">
            <ItemTemplate>
                <asp:LinkButton runat="server" ID="lbFolderItem" CommandName="OpenFolder" CommandArgument='<%# Eval("Name") %>'></asp:LinkButton>
                <asp:Literal runat="server" ID="ltlFileItem"></asp:Literal>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="FileSystemType" HeaderText="Type" SortExpression="FileSystemType" />
        <asp:BoundField DataField="LastWriteTime" HeaderText="Last Modified" SortExpression="LastWriteTime" />
        <asp:TemplateField HeaderText="Size" SortExpression="Size" ItemStyle-HorizontalAlign="Right">
            <ItemTemplate>
                <%# DisplaySize((long?) Eval("Size")) %>
            </ItemTemplate>
            <ItemStyle HorizontalAlign="Right"></ItemStyle>
        </asp:TemplateField>
        <asp:CommandField HeaderText="Rename" SelectText="Rename"
            ShowSelectButton="True" ButtonType="Link"/>
        <asp:CommandField HeaderText="Delete" DeleteText="Delete"
            ShowDeleteButton="True" ButtonType="Link" />
    </Columns>
 </asp:GridView>

public void delFile(object sender, GridViewDeleteEventArgs e)
    {
                     //I have got error:
         //System.ArgumentOutOfRangeException:
         //Index was out of range.
         //Must be non-negative and less than the size of the collection.
        string filename = gvFiles.DataKeys[e.RowIndex].Values[0].ToString(); //on this line


        string path = Server.MapPath(ConfigurationManager.AppSettings["path"] + "/" + filename);
        //actually do not delete. Add a suffix in order not to list it to the user
        File.Move(filename, filename + "_del");

        PopulateGrid();
    }

    public void renFile(object sender, GridViewSelectEventArgs e)
    {
         //I have got error:
         //System.ArgumentOutOfRangeException:
         //Index was out of range.
         //Must be non-negative and less than the size of the collection.
        string filename = gvFiles.DataKeys[e.NewSelectedIndex].Values[0].ToString(); //on this line

        string path = Server.MapPath(ConfigurationManager.AppSettings["path"] + "/" + filename);
        //just for experiment
        File.Move(filename, filename + "_ren");

        PopulateGrid();
    }