Drupal is an Easy one-click install, which means that it’s not installed in your home directory and you won’t be able to access it. To do the mods you want, you’ll have to install Drupal manually.
The One Click page has this to say about Easy installs:
(In easy mode, you cannot access the files for the installation (so can only use the (plenty of) themes/plugins/languages we’ve included), but installation, upgrades, and maintenance is 100% handled for you!)
And in bold red print:
WARNING! In easy mode you cannot install your own plugins or themes (though there are a number included). To have full customizability, pick advanced mode below.