Some have trouble getting the update with mac app store so you can get the Sierra DP4 via browser instead with these links:
firmware update: http://swcdn.apple.com/content/downloads/27/20/031-69394/q9txj420gnt6s9fzee346qdsexvuv1ywaw/FirmwareUpdate.pkg
full bundle update: http://swcdn.apple.com/content/downloads/27/20/031-69394/q9txj420gnt6s9fzee346qdsexvuv1ywaw/FullBundleUpdate.pkg
Don’t just run the installers individually. They will stop you doing that with an error message.
Instead put them into /Library/Updates/031-69394 and restart. Then go to updates tab in mac app store and click update.