This doesn't appear to be a DNS question. It's more of a web server question. Which server are you using? Apache or IIS, probably.
If it's apache, then you just do a:
DocumentRoot /path/to/your/www/dir
Most likely that will be in a VirtualHost directive.
If it's IIS, then you should switch to apache.... 😃 j/k. If it's IIS, I can't help. Sorry.