It's easy with a WinSCP .NET assembly. Just use a Session.ListDirectory to enumerate all folders and than call a Session.PutFiles for each.
https://winscp.net/eng/docs/library_session_listdirectory
https://winscp.net/eng/docs/library_session_putfiles

How do I use scripting to upload a single file to each of the sub folders in my ftp?

I have a big folder called "users" , and its sub folders are called "Mary","John","Peter",etc.

There are hundreds of sub folders and I don't want to enter their names one by one.

Is there a simple way to do it? Thanks.