How to open and edit files on ftp server?

I am making a local intranet site at work, and one function it needs to have is the ability to open up files on our shared database and edit them. Once the user is done editing and hits save, it should save to the same spot it was opened from, kind of like updating the file. I read about using the ftp_get() function, but I don’t understand how I would go about saving it back to the same spot on the server automatically.