You can change the route in the global.asax.cs
Default route is
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Home", action = "Index", id = UrlParameter.Optional },
new[] { "Nop.Web.Controllers" }
);
This route will tell you execute in the HomeController, there is Index action (function) and return the view defined with the same name under the Views. View path will be Views/Home/Index
In order to change that you should add a welcome function (just copy the Index function and rename with welcome and paste it into the HomeController).
Then you can change your routing as bellow.
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Home", action = "Blog", id = UrlParameter.Optional },
new[] { "Nop.Web.Controllers" }
);
Dont forget to create your Blog view under Views/Home as Blog.cshtml
Thanks