Installation: Download the msi-package for Windows from the Psoft site and run it.
Update: Download the msi-package for Windows from the Psoft site and run it. If it was your first installation, do not forget to specify SMTP and sendmail_from keys in your php.ini file (in the Windows folder).
After you install the package, it will be added to the list of installed packages in your admin Control Panel, in the Settings->Packages menu:
This is helpful to find out whether all package files are installed correctly.