Where to upload and download the file using filezilla?

The file can be uploaded anywhere on the QBox Server as long as it is accessible for download. If we are to suggest one particular directory, you can upload a file from your desktop client to the /home/crio-user/workspace/ftp_server directory (make sure you have created this directory on the QBox Server and the file size being uploaded is less than 1 MB) and download the file from there to your mobile client.