I think you're little bit confused

1) i am nt getting what method should i use for uploading the file??
You are speaking about upload a file on vsftpd server, then you have to use FTP protocol.
See QFtp class. It has the QFtp::put method that allows to send file to a FTP server.

2)am using vsftpd server. can u tel me where is the uploaded data stored on this server????
it depends from vsftpd server configuration.