To install Boot Camp Support Software 5.1.5621, follow these steps: Boot Camp Manuals and Downloads - Apple Support (IS)
: Early 2009, Mid 2010, Mid 2012, and Late 2013 models. boot camp support software 515621
: Installs the Boot Camp Control Panel in Windows, allowing users to set the default startup disk and adjust keyboard/trackpad settings. Installation Guide To install Boot Camp Support Software 5