That page URL:
https://winscp.net/eng/docs/library_example_moves_files_keeping_directory_structure

And there's a link that points to the documentation:
https://winscp.net/eng/docs/ui_pref_commands#extensions
There it is explained that you go to Preferences > Commands and click Add > Add Extension.

Thank you for fast reply but I'm totally lost... I would like to install addon (PowerShell). There is:

You can install this script as an WinSCP extension by using this page URL in the Add Extension command.

But which URL should I use? Where to use it?

See Recursively move files in directory tree to/from SFTP/FTP server while preserving source directory structure.

Hello. I have folder on my PC. There are many subfolders in this folder.
I want to upload all files from those subfolders to FTP where is the same folder structure. After succesfull upload I want to delete all files in all folders on my PC but preserve folders.
Is this possible? If yes, could you please show me script example?

Thank you very much.
Jan