Reason 10 and later comes with optional content (Rack Extensions and ReFills) that you can download separately, either during the first launch of Reason 10, or at a later point.
To download the optional content, proceed as follows: (There is also a Quick Tip video that describes this, here.)
Note that this procedure requires Internet connection!
1. Select "Manage Content" from the Window menu in Reason to bring up the Manage Content window:
2. Select the item(s) you wish to install.
3. Click the "Install" button.
Alternatively, skip step 2 and 3 and click the "Install all" button to install all items in the list in one go. Progress bars show the download of the items:
4. After download, restart Reason for the downloaded and installed items to become available.
Rack Extensions become available on the respective palettes in the Reason Browser - in the "Reason Devices" section. ReFills become available in the Locations section in the Reason Browser.
The additional content is stored in sub-folders in the Music > Propellerhead Content folder on your computer. Rack Extension devices are stored in the "Optional Devices" sub-folder and ReFills are stored in the "Optional Refills" sub-folder.