Apple
How to Downgrade macOS High Sierra to macOS Sierra
If the macOS High Sierra problems are too much, you can downgrade from High Sierra to macOS Sierra without losing much time or much data. This guide will show you how to go back to macOS Sierra from macOS 10.13 if the problems are too much.
There is no time limit to downgrading, but you will need to make sure you have a Time Machine Backup on macOS Sierra if you want to do this the easy way. This gives you a nice cushion of time to try the macOS High Sierra update if you want, and still go back.
Apple delivers many new features, but there are a lot of macOS High Sierra problems out there frustrating owners. If you already updated and you can’t fix your macOS High Sierra problems, you may want to go back to macOS Sierra until the macOS 10.13.1 update arrives with more fixes and a hopefully more stable operating system.
How to Go Back to macOS High Sierra

How to downgrade macOS High Sierra to macOS Sierra with a Time Machine Backup.
You can downgrade from macOS High Sierra to macOS Sierra in a number of ways, but the best way, and the easiest, is to use a Time Machine Backup made before you upgraded. This is why we recommended a recent backup before you upgraded. Before you start this process, we recommend making another backup on macOS High Sierra, so you have a recent copy available if anything goes wrong.
When you are ready to downgrade, shut off your Mac. Now, turn it on and hold Cmd + R until it boots into recovery mode which looks like the screen above.
Click on the Restore From Time Machine Backup option and then on Continue. On the next screen you will need to choose your Time Machine Backup drive. Make sure it is plugged in. If it isn’t, plug it in and check again. If it still doesn’t show up you may need to restart again and try with it plugged in.

Choose your Time Machine Backup drive to start the downgrade.
Now you need to choose the backup you want to restore to. For most users this will be the last backup on macOS Sierra. This will show up as macOS version 10.12.6, or some other 10.2.x version number depending on what updates you installed before macOS High Sierra.

Pick the macOS Sierra backup to restore to.
Choose the backup and then click Continue. Next, you will choose the location to restore that backup to. In most cases you will choose Macintosh HD. This will remove macOS High Sierra and put macOS Sierra on your Mac int eh same state it was on the day and time you made that backup.
Once this is done, you will need to wait a little while for the Time Machine Backup to restore to your Mac and then you will be able to use macOS Sierra. Do not force your Mac to restart even if you think it is frozen. This can take some time and it may appear to hang up, but it should keep going after short pauses. Make sure your Mac is connected to power.
