Question: I am trying to do a clean install from Yosemite to High Sierra. The boot installer is only downloading 19.5MB instead of the 5GB's. Any help would be appreciated.
You need to create a bootable installer USB drive. Here is what you must do:
1. Download macOS Sierra from the Mac App Store
2. After the download has finished, plug in your USB drive (at least 8 GB or more). Name it MyVolume
3. Run the following command:
sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app
4. Type in your administrator-password. There are no digits showing that you are typing your password in. Press ⏎.
5. Press "y". Remember, all of the data on the USB drive will be removed.
6. Once the process has finished, shut down your Mac.
7. Boot your Mac up using ⌥ down.
8. Choose the USB drive called "Install macOS Sierra" as your startup disk.
9. Choose "Install a new copy of macOS". The installer will guide you through the installation process.
10. Have fun with your new macOS Sierra!
MacBook Pro with Retina display