Download Filezilla
Install Filezilla.
1. Once installed, open the Site Manager (File / Site Manager)
2. Click on "New Site"
3. Fill in your account details, as follows:
Hostname: ftp.yourdomain.co.uk
Port: Port 21
Logon: type: Normal
Username: your eight-letter cPanel username
Password: your cPanel password
3. Click on "Connect".
4. Now click on “public_html” in the right-hand window and you can then drag and drop the files on your computer (displayed in the left hand window) over to the right window within the public_html folder.
Full documentation for Filezilla is available here: http://wiki.filezilla-project.org/Documentation