If true, then a major update will be required. To avoid this and jump directly to the current version of macOS, creating a bootable USB stick can be quite useful. If you use multiple Macs, such a stick can save you from downloading the install app from the Mac App Store multiple times. In the following instructions we would like to explain to you which conditions must be fulfilled and what else is to be observed.
Before you create a bootable media with macOS High Sierra, you should make sure that the USB stick, SD card or external USB drive has at least 12 GB of free space features. This medium also should not contain any data that should not be deleted. We therefore recommend that you buy a USB stick only for the purpose of using it as an installation stick for the Mac. Since future updates may be larger than the previous ones, you should make sure that you buy a stick with enough space when you buy it, even if you want to use it for future updates of the Mac operating system. Otherwise, Apple will provide you with all the tools you need to create bootable USB sticks.
How to create a bootable USB flash drive with macOS High Sierra
Before you start the future installa- Plug in Stick, first download macOS from the Mac App Store. Once the download is complete, the installer opens. Close it again and check if the file is in the Applications folder. This folder can be found via the sidebar in the Finder. The installer should be called “Install macOS High Sierra.app”, but appears here as “Install macOS High Sierra”. If it has been moved to another location, move it to the Applications folder to easily copy the steps below to your bootable USB flash drive.
Now insert your USB stick or the SD cards into your Mac. New “MacBook Pro” models, however, lack the SD card slot and you may need a USB-C adapter. After your future boot-stick is connected, start the Disk Utility via Programs> Utilities. Then select the storage medium from the sidebar. Now click on “Delete”. Enter “USB” (without quotation marks) as the name and select “Mac OS Extended (journaled)” as the format. Set the scheme to “GUID Partition Table” and then click “Delete” to completely empty the USB flash drive.
Now open the Terminal App. It is also located under Programs> Utilities. Now enter the following line to move the installation app to the USB stick and turn it into a bootable installation stick with High Sierra:
sudo / Applications / Install macOS High Sierra .app / Contents / Resources / createinstallmedia –volume / Volumes / USB –applicationpath / Applications / Install macOS High Sierra.app –nointeraction
Now press Enter to get the stick to create. If necessary, your Mac will also require your system password so that the installer files can be transferred. Of course, the duration of this process depends on the writing speed of your stick and may take a few minutes.
How to use the created USB stick to install High Sierra
Please note that data may be lost during a new installation or Clean Install. Always back up all important files before starting the installation program.
To use the USB stick for the installation of macOS, first insert it into a free USB slot. Now start your Mac while holding down the Alt key. This does not boot Apple’s Mac OS directly, but initially opens the Startup Manager. Here you can now select the start volume. Click macOS High Sierra and press Enter. After a short moment, the operating system is booted from the USB stick. Follow the instructions on the screen to complete the installation.