How to save your backup file using FTP
Download and install a copy of FileZilla
Select the Site Manager to add a new site
Fill in the fields that pertain to your domain
Your website is in the public_html directory (but the backup is not)
If you're running Joomla, this is what your Joomla directories look like
The backup files will be in the root directory (never in public_html)
When you finish downloading the backup file, delete it from the web server
READ THIS
Be very careful with FTP It's very easy to delete an entire directory with a few clicks. Also, never leave the backup file only on your local hard drive. Burn it to a CD and tuck it away in a safe place in a location other than where your hard drive is. If the backup was for a client, mail them a copy of the CD.