7. Back up your files
There are no backups except those
which we make for ourselves. Backing up is generally a very good idea before making any major change to your operating system but particularly important if you want to roll back to the previous version of macOS.
If you use an external drive for Time Machine, make sure it’s connected to your Mac and then click on Apple > System Preferences > Time Machine. Check the date of the latest backup to be sure your file system is current and make a careful note of the date and time. This is important if you want to restore your system later.
If you prefer to start a back-up manually ensure that the option marked ‘Show Time Machine in menu bar’ is ticked. Click the icon at the top right and select Back Up Now. Remember that if you choose to restore your system from this point after upgrading to High Sierra, any changes you’ve made will be lost.
If you use another backup method such as syncing files in your Desktop and Documents folder to iCloud, make sure that any important data is moved there.
Remember that if you don’t use Time Machine, you won’t be able to restore applications and saved data purchased outside the Mac App Store. Either run a Time Machine backup now or make sure you have the necessary serial numbers/login information for apps so you can reinstall if necessary.
And don’t forget that other users on your Mac may have installed applications using their own Apple ID. Check to make sure they know their Apple ID password before upgrading. You can never be too safe when it comes to backing up!