There are three key aspects when you are considering a downgrade from macOS Sierra to El Capitan. These are as follows:
- First You will have to Erase the macOS Sierra from your Mac
- Next you will have to Re-install El Capitan
- Check that your System is stable
Usually this process is pretty easy and safe if you had chosen a second partition for using the beta install. It is always a good idea to do so if you are trying to install a beta edition of the OS X.
Lets proceed with the detailed steps for each of the above milestones. Please make sure that your machine is connected to a wi-fi with internet access before your proceed.
Erasing the existing macOS Sierra
- Restart your Mac from the menu
- Hold Down Command +R keys together upon hearing the chime and hold the keys till you see the Apple logo appear on the screen. This launches your Mac into the recovery mode
- Select Disk Utility from your OS X utilities
- Select the indented volume name of your startup disk from the left side of the Disk Utility window, then click the Erase tab.
- Type in Macintosh HD for the name as Mac OS Extended from the format list and then choose Erase
- Close the Disk Utility window
Reinstall El Capitan
Now that the macOS Sierra has been erased from your drive, you will need to re-install the OS X El Capitan.
- Re-install OS X from OS X utilities and choose the OS X El Capitan Installer.once the process is complete, restart the Mac.
- Invoke Recovery mode while the Mac is starting up by pressing together the Command + R keys.
- Open your OS X Utilities. From your OS X Utilities menu, click Restore from Time Machine Backup. We are assuming that you had made a complete backup before installing the macOS beta on your machine.
- Select your Time Machine backup disk
- Select the backup you want to restore from
- Click Continue and follow the instructions to reinstall OS X and your backed up files.
Check Your System
- At this point, you have erased macOS Sierra and re-installed El Capitan. Restart your Mac and you should be all set to go.
- In the case, you run into issues in starting your Mac or Macbook after the El Capitan re-install, you may have to check some of your kext settings if you hadn’t already taken care of it prior to the beta install.