- Download the 5GB macOS 10.13 (High Sierra) Installer
- Prepare a USB Drive using Install Disk Creator
- Boot holding Option key and install High Sierra from the USB Drive
If you want to try the newest macOS 10.13, aka: High Sierra you can perform a clean install to get the best overall user experience. If you have existing data always back it up or, going forward keep it always synced to some cloud drive – such as Apple’s iCloud service which is already included in macOS since Sierra released. It’s a convenient way to keep your Desktop and Documents folders primarily in the cloud…then synced to your local hard drive. If you have multiple Macs it also allows you to carry those files to each of your systems.
Full Procedures can be found here: