I get a message stating that SyncServices Agent must be closed to update the software in OS X El Capitan. How do I do this?
Give this a try. Hopefully it will solve your problem.
(1) Open Finder/Applications/Microsoft Office 2011/Office
(2) Drag SyncServicesAgent.app to the desktop (this keeps it from restarting!)
(3) THEN open Finder/Applications/Utilities/Activity Monitor.app
(4) Find SyncServicesAgent in the list and quit it.
(5) Click the Continue button on the installer pop-up.
(6) When the application finishes installing, drag SyncServicesAgent.app back to Finder/Applications/Microsoft Office 2011/Office