If you do not have an ftp client (or if you are not sure what those are), download and install an ftp client on your machine. Filezilla is a free client available for multiple Operating Systems.
Once you have the ftp client installed (assuming it is Filezilla), open it and enter the hostname, username and password as sent to you and click connect/quickconnect. It should connect to the server and in the panes below you will see files on your local machines. Browse to reach the files you need to upload, right click and select upload. Wait until the upload is complete and successful before closing the ftp client.