Just delete the directory. If you used the full SQL server, also delete the database.
I don't believe it is that simple.
For example I had 0.9 installed on my Windows 7 (64 bit) test machine with IIS. Orchard was installed at C:\inetpub\wwwroot\orchard\
Next I deleted the orchard directory.
Finally I went into IIS Manager (via Control Panel, Administrative Tools) and Orchard still shows (although the directory is gone).
Don't I need to remove the application in IIS Manager?