Sharing files from a Windows 10 machine to Ubuntu 16.04lts on another network?

I have a plex server on my windows 10 desktop and I recently set up a second server at a friend's house. What would be the best way for me to share movies from my desktop to a remote ubuntu machine? I know it is possible to use port forwarding to map a remote network drive, but then someone would have to get into the ubuntu machine to copy movies from the network drive to the local drive. I want to stay away options like google drive or dropbox because I don't want to pay for storage over 15gb and they have slow internet. Also, someone would still need to get onto the computer to download the movies from the cloud