The site file upload functionality is not supported with all pre-packaged themes.
HTML4-based uploads are not supported in this release. HTML5’s File API, Silverlight, or Flash will be required for uploads. (When using IE, Flash or Silverlight is required because IE does not support the HTML5 API.) For general page rendering, both HTML4 and HTML5 are supported.
To upload a site file:
Navigate to Control Panel Dashboard > System Administration > Site Administration > Site Content > Site Files.
Enter the path to the file you want to upload in the Upload a new file in this folder text field or browse to the file by clicking Browse.
Click Upload. The uploaded file displays in the list.