Reset or Uninstall Yosemite Server
You can reset just the Websites service in OS X Server with the following command:

sudo serveradmin command web:command=restoreFactorySettings


Make sure the Websites and Wiki services are off when you run this command.

Uninstalling OS X Server will, by default, retain all configuration files so that reinstallation keeps all data, however you can delete the Server folder to reset all the data.