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Sep 30, 2016 your Mac; MA c Book pro 15 in c h late 2008, is not supported for Sierra. The link in my previous reply listed: MacBook Pro (Mid 2010 or newer) SInce neither Yosemite or El Capitan are no longer available from the Mac App Store and you have not previously downloaded them, if you go to an Apple store they may be able to download EL Capitan for you since that is the last version your Mac. OS X El Capitan Security Updates 10.11.6 - Security Updates for OS X El Capitan. Download the latest versions of the best Mac apps at safe and trusted MacUpdate.

Apple OS X El Capitan, the latest version of the Mac operating system, builds on the groundbreaking features and beautiful design introduced in OS X Yosemite, refining the experience and improving performance in lots of ways that you’ll enjoy everyday. El Capitan introduces enhancements to window management, built-in apps and Spotlight search, and makes everyday activities - from launching apps to accessing email - faster and more responsive. Metal, Apple’s breakthrough graphics technology, is integrated into El Capitan delivering system-wide performance gains and enabling games and pro apps to tap into the full power
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What's New in OS X El Capitan Security Updates

Version 10.11.6:

Note: This update is provided for all users that have an earlier version of OS X 10.11.x already installed on their machine. Please note that macOS or OS X downloads or installations typically need to be handled via the App Store.app or directly from Apple.

Resolves an issue that may prevent settings from being saved in accounts with parental controls
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Requirements for OS X El Capitan Security Updates

OS X 10.11 or later

OS X 10.11.6 Update Combo (1.54 GB, OS X 10.11)
OS X 10.11.6 Update Delta (717.9 MB, OS X 10.11.5)
OS X 10.11.5 Update Combo (1.53 GB, OS X 10.11)
OS X 10.11.5 Update Delta (759.1 MB, OS X 10.11.4)
OS X 10.11.4 Update Combo (1.94 GB, OS X 10.11)
OS X 10.11.4 Update Delta (1.58 GB, OS X 10.11.3)
OS X 10.11.3 Update Combo (1.47 GB, OS X 10.11)
OS X 10.11.3 Update Delta (662.3 MB, OS X 10.11.2)
OS X 10.11.2 Update Combo (1.4 GB, OS X 10.11)
OS 10.11.2 Update Delta (1.4 GB, OS X 10.11.1)
OS X 10.11.1 Update Delta (1.19 GB, OS X 10.11)

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The Latest OS X Yosemite with version number 10.10.4 is able to be downloaded since today. After a couple of weeks in beta version which can only be installed by Apple membership developers who has registered by paying $99/year. OS X Yosemite 10.10 is compatible with these following Mac series:

iMac (Mid-2007 or later)
MacBook (13″ Late 2008 Aluminum, Early 2009 or later)
MacBook Pro (13″ Mid-2009 or later)
MacBook Pro (15″ Mid/Late 2007 or later)
MacBook Pro (17″ Late 2007 or later)
MacBook Air (Late 2008 or later)
Mac mini (Early 2009 or later)
Mac Pro (Early 2008 or later)
Xserve (Early 2009)

There are 2 options that you can do to update OS X Yosemite 10.10.4:

By downloading update through App Store
By downloading through Apple Support

Actually, the update process is very easy, but not everyone knows how to update OS X safely.

Here, we want to discuss with you about how to update Mac to OS X 10.10.4 safely. We want to make the update process runs smoothly and avoid the problem which cannot be predictable even by Apple itself.

How to Update Mac to OS X 10.10.4 safely

Apple suggests to always update our device because it can give us the advantages like bug fixes, feature improvements and so on. But we want to be a smart user and not only following what Apple instructed. The information that you can get as a user is “Release Note”. It’s an official note and complete related to anything about update which is launched by the party who launch update.

Release Note can you read when the update process is about to be done to give the complete information. From this information, you will know whether the update is fit with your need or not, or the possibility of certain capability issue which can make your productivity is disturbed. I will re-write Release Note about OS X 10.10.4 for you to be read and learnt.

Release note

Complete release notes of the OS X 10.10.4 software update

Improves networking reliability
Improves Migration Assistant reliability
Addresses an issue that prevented some external displays from functioning properly
Improves the reliability of upgrading iPhoto and Aperture libraries to Photos
Improves reliability when syncing photos and videos to iCloud Photo Library
Addresses an issue that could cause Photos to unexpectedly quit after importing some Lecia DNG files
Resolves an issue that could delay outgoing email messages in Mail
Fixes an issue where a website could prevent the user from navigating away by presenting repeated JavaScript alerts in Safari
Enterprise content

For enterprise customers, this update:

Addresses an issue where OS X systems bound to directory services could stop responding under certain conditions
Adds the ability to create mobile accounts with the createmobileaccount tool
Fixes an issue in Profile Manager that could allow a user to install pre-release software even when the setting is disabled

Add new security content

Great Preparation for update safely

Mac Software Update 10.10

The preparation for update safely is rare to discuss because it seems a simple tips but it really useful for you

Prepare a minimum 5GB of free storage on your Mac. If you need to reduce data on Mac, you can transfer the data to HDD External first (this is need for MacBook Air with small storage size).
Backup all data on Mac first: You can manually copy data to external or backup via Time Machine
Do: verify disk and repair disk permission. Go to Disk Utility, choose your HDD and on First Aid tab, choose verify disk. If it’s Ok, continue by clicking Repair Disk permission. If verify disk shows need to repair disk, refer this guide on Section Try Disk Utility to repair disk via Recovery HD

Restart your OS X
Close all application
Even though is not a must, i suggest you update all applications first.
Connect Mac with a fast WiFi connection.
Connect Mac with adapter charger during the update process.

Steps to Update via App Store

Click Apple Menu  on menu bar
Choose App Store
Choose tab Update
App Store will check the latest update and you will see OS X 10.10.4 update with its release note. Click Update. App Store will download OS X 10.10.4 update, tap Restart.

Mac will log out and install the update then restart if the update process has done.

Steps to download Update via Apple Support

Check your OS X Yosemite version in Apple Menu  >> About this Mac.

Open your favorite browser, go to Apple Support download Mac OS

Update Os On Mac How To

Choose OS X Yosemite 10.10.4 Combo Update. It fits for you who has the older version than OS X 10.10.3.
Choose OS X Yosemite 10.10.4 Update if your Mac has OS X 10.10.3 version.
The download result is in form file OSXUpdCombo10.10.4.dmg or OSXUpd10.10.4.dmg
double click dmg file and then double click OSXUpdCombo10.10.4.pkg or OSXUpd10.10.4.pkg
Let the update process running, mac will log out and install the update then restart if the update process has done.

If you have any questions related to this update

Manual Updates Mac Os10