There is not currently a "delete" function. You can just set the status back to "Draft" and it will not appear any longer in our sitemap files or onsite. The steps to do this are:
1. Select the site you wish to set to "draft" from the Sites screen in the Account section
2. In the Site Manager, click on the Setup icon
3. On the Setup > General screen, you will see an option for Site Status. Simply toggle that setting back to Draft.
We also suggest that if you have setup a CNAME or A Record with your domain host that you delete this. This will ensure that your URL does not try to redirect to LaunchRock any longer.