FTP maybe is not a necessity. Have you considered using dolphin (or any other file manager on ubuntu) and exporting it's display trough the ssh tunnel ? It will spare you the FTP administration, ports, user credentials, etc...
You need a local X server for this, provided by default on linux, but on windows you should install xming which is free.
ssh -Y remotemachine -l root (or any other sudoer)
"dolphin" is like the file explorer for linux, it's a gui for moving files.
"ssh tunnel" means that the program that you start on the server will be displayed on your machine: ie it will popup a graphical interface on your screen, not on the server screen.
"local X server" is the server that receive the informations from the program you have started. Xming is a example of an X server for windows. You install it on your windows client and it waits for a connection incoming from your server.
1) download and install Xming for windows. Also download and install fonts for Xming. Both are free, google for it. Don't forget to run it afterwards, it will appear with the icons near the windows clock. No window will be visible yet at this step.
2) open putty but before starting your connection, enable the X forwarding, it's in the ssh options of putty, in the left tree, near the bottom. Save the config and start the connection like you did usualy. This setting is totally transparent, if you don't use grapical interface in a putty session it won't make any difference if the tunnel is enabled or not.
3) try your tunnel: from your shell start any program that have a GUI interface, it should popup on your windows desktop. for example start nedit, of gedit. If it popup then you're ready. Now you need to start this program as root. try to "sudo nedit" (then browse to the file you want to edit from the nedit file menu). If it doesn't work you may have to "sudo -s" first, then to start "nedit". nedit and gedit are typical, very light, editor programs. Maybe you have another one installed in ubuntu that you prefer,you can use any program you want, it's not important.