You can not convert asp.net to SharePoint. First of all, because SharePoint is not something you can convert to. It is a CMS, it is a product, a platform, and many more. And SharePoint is working on top of ASP.NET.
But you can convert ASP.NET
site to Sharepoint
site:
Converting an ASP.NET site into a SharePoint site[
^] or application to application:
http://aymanelhattab.com/2014/01/11/converting-asp-net-web-applications-into-sharepoint-apps-using-visual-studio-2013/[
^]
So, you have some ways to convert generic asp.net
something to SharePoint
something. But not asp.net to sharepoint. That makes no sense...