You can uninstall Plesk using ‘Add/Remove Programs’ wizard, or by
running Plesk installer program and selecting the Uninstall option.
Then you should manually delete the folders %plesk_dir% (usually
c:\program files\SWsoft\Plesk) and %plesk_vhosts% (usually
c:\inetpub\vhosts).
Once done, install Plesk again.