You can list the File's with the FileSystemStorage API, the FileTree has an example but its pretty buggy at the moment
http://code.google.com/p/codenameone/issues/detail?id=97To upload a small file you can just add its content as an argument to a post request, just create a ConnectionRequest set the URL and addArgument with the file content.
For larger files you will have to create a multipart-mime upload client/server implementation. You can just derive the ConnectionRequest and implement the logic by overriding the appropriate methods. Since I didn't do this in Codename One I don't have specific pointers I can give you there, we probably should offer something like this builtin in the future (as we should offer many other things too).