Here are a few FTP software recommendations:
WS_FTP LE: WINDOWS
Here is a free version which works well. It is technically only for students, but it is such an old version, I wonder if they would really care at this point. Does NOT support FTPS (FTP over SSL security). Use at your own discretion. DOWNLOAD.
FILEZILLA: WINDOWS, MAC, LINUX
This one is more complicated to use, but works well and, more importantly, supports FTPS (FTP over SSL, for encrypted, secure connections). MORE INFO.
FIREFTP: WINDOWS, MAC, LINUX (requires Firefox)
This is a plug-in for Mozilla Firefox. We've not tried it yet, but a user reports it works well with our service. MORE INFO.
We are told this one is a great free FTP client for Apple Mac users. MORE INFO.
Also, there is a nifty FileManager built right into your cPanel, that you can use to upload and manage files on our server.
For information on SFTP (FTP via SSH), see THIS ARTICLE.