upgrade to Sierra, 10.12
How to upgrade MacBook Pro from 10.11.6 El Capitan to 10.12 Sierra.
Downloaded the update from Apple, tried to install, but didn't work.
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What did you download from Apple.
Did you do this.
Open your Safari browser and click on the link below.
How to get old versions of macOS – Apple Support
Go to Download macOS and click on macOS Sierra 10.12
This downloads InstallOS.dmg to your Downloads folder.
The next section can only be done on a mac that is capable of running Sierra,
a mac that came preinstalled with an OS later than Sierra will refuse to do the next bit.
When downloaded open to get InstallOS.pkg, double-click on
that and an installation window will open, read and follow the prompts,
this does not install Sierra but uses the InstallOS.pkg to create the
Install macOS Sierra.app which you will find in your Applications folder.
(If the installation window asks which disk you want to install to, you must pick
the disk that you are booted to at the time. Not any internal or external disk that
you want to eventually install Sierra on, that is for later.)
To start the installation of Sierra double click on the Install macOS Sierra.app.
The copy of the install app self deletes after installing Sierra, so make sure you keep a copy of the InstallOS.dmg
if you need it in future, or you could just make a copy of the Install OS X Sierra.app prior to installing and moving it to
an external drive for safe keeping.