Purchase or download Reason Refills. There are Refills available for free and for purchase at the Propellerhead website. In order to access them, you have to create an account on the website using your email address and the Reason product code that comes included with the software. Independent sites, such as ReasonReFills, also sell Refills, and sites like Reason Station provide thousands of user-created Refills.
Move your refills into the Reason folder on your computer. Every program comes with its minor bugs, Reason 4 being no exception. Unlike samples or individual synthesizer patches, Reason has difficulty locating the Refills you used on a project when re-opening it. Under your main hard drive, the Reason folder should be located under "Program Files > Propellerhead > Reason."
Open Reason and create a new song. Right-click on the rack window, the part of Reason that has all your synthesizers, and create a new device. Choose a device that your Refill is intended for; for example if your Refill contains nothing but drum samples, use the ReDrum Drum Computer. Left-click on your device's folder button to load Refill patches into your device. The default setting for this load window should direct you to the Reason folder that you moved your Refill into. Double-click on the Refill, and your list of packaged synth patches should be available.