ecohost co-op | UK based web hosting powered by renewable energy

EITHER: Log in to your Plesk control panel and use the "File Manager". This can be found in the "Tools" menu as "Manage Files on Domain".
To upload files, click on "Add New File"

OR: Using an ftp client, such as Filezilla, log on to your ftp server with the ftp details you've been given. These should include ftp host address, user name and password. Your html files are in a folder called <httpdocs>. This is where your website files should be stored.