How to set default page asp.net

Besides Felipe's answer, you can also do this from IIS.

Select Admin Tools --> IIS Manager --> Select your website from the list. Click on Default Document on the right hand side and Click Add. Move the entry to the top of the list using the arrows. You are done.

This will be overwritten each time you publish your site, however.

ASP.NET WebForms

On the web.config file, try this to use the clear tag before:

<system.webServer>
  <defaultDocument>
    <files>
      <clear />
      <add value="Pages/Home.aspx" />
    </files>
  </defaultDocument>
</system.webServer>

Take a look here: http://www.iis.net/configreference/system.webserver/defaultdocument

ASP.NET MVC / ASP.NET CORE

Depending of the version of asp.net mvc you are using, you can have it on a different file (~/Global.asax.cs in v3 or older or ~/App_Start/RouteConfig.cs in v4 or newer). In both cases, you will see something register the routes, because asp.net mvc uses routes instead files like webforms. So, you can change the default values:

public static void RegisterRoutes(RouteCollection routes)
{
    routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

    routes.MapRoute(
        name: "Default",
        url: "{controller}/{action}/{id}",
        defaults: new 
        { 
            controller = "Home", // default controller
            action = "Index",  // default action on the controller
            id = UrlParameter.Optional
        }
    );
}

It is similar on the ASP.NET CORE.

Take a look here: http://www.codeproject.com/Articles/624181/Routing-Basics-in-ASP-NET-MVC