as it says on that link (above) = "This feature is only available from the cPanel x3 theme"
if you are currently using the [ x10hosing's Basic ] cPanel theme - try [ Switch Theme ] near the top-right of the page - and click on [ Switch to cPanel x3 ]
Try removing files and/or folders you don't really need on your account. (Like backups - they can [and should] be stored locally, cloud storage, external drives, ...)