Web サイト プロジェクトのリネーム
Using some of your information, I found that IISExpress had an "applicationhost.config" file located in my %UserProfile%\Documents\IISExpress\config directory. Opening that file showed all the sites. In my case it already had the name of the site in it that I wanted in my solution, so the solution kept adding a (1) to the end of the website. Changed the name in there and removed the dup, restarted the solution and it worked fine.