To re-install WSUS with a clean database i.e. no previous configuration:

Run Windows Powershell as Administrator and use the following commands:

  • Uninstall-WindowsFeature -Name UpdateServices,Windows-Internal-Database -Restart

  • Post restart, delete EVERYTHING in the C:\Windows\WID\ (for Win 2012 r2) folder.

  • Then run the following command to re-install WSUS:
    Install-WindowsFeature UpdateServices -Restart

This only works on PowerShell 3 or higher.

UPDATE
I had to run the postinstallation tasks manually via Powershell using the WID db, if using SQL you need to add in sql_instance=

C:\Program Files\Update Services\Tools\WsusUtil.exe content_dir=”<<dir of update download location>>

creds: https://serverfault.com/questions/449914/how-to-completely-wipe-wsus-and-start-again