A method of upgrading a medical device having a controller that controls operation of the medical device according to an operating routine executed by the controller. Upgrading the medical device includes communicating an external device, such as a conventional computer, with the controller. An external access key is provided to the external device and compared to an internal access key provided by the medical device. Upgrading of the medical device is enabled if the two access keys match. Upgrading includes modifying or rewriting the operating routine stored in the medical device. A medical device manufacturer, supplier, or seller controls the distribution of the external access keys, thereby providing the ability to track the medical devices being upgraded and the upgrade provided to that device.