The FTP responder in RepRapFirmware supports the following FTP commands:

• ABOR
• CDUP
• CWD
• DELE
• FEAT
• LIST
• MKD
• NOOP
• PASS
• PASV
• PWD
• QUIT
• RETR
• RMD
• RNFR
• RNTO
• STOR
• SYST
• TYPE
• USER

See one of the many references on the Internet for a description of what they do.