I have just installed ES File Explorer on my Samsung, and started the Remote manager
I opened a FTP client on my PC and could connect to my tablet.. But I can't write files only read? Is this a bug or do I have to pay to get write access?
Not necessarily, I have the same setup on my devices using both MiXplorer and ES explorer. The ftp server runs fine with read/write access (even on non-rooted device).
Perhaps your OS doesn't allow anonymous logins to have write access, in which case you need to configure a password authentication on your ftp server: