Out of storage while updating MacOS

Did you erase the Drive?

1. Start up from macOS Recovery

To start up from macOS Recovery, turn on your Mac and immediately press and hold one of the following combinations on your keyboard. Command-R is generally recommended, especially if you never installed macOS Sierra 10.12.4 or later.

Command (⌘)-R Install the latest macOS that was installed on your Mac.

Option-⌘-R Upgrade to the latest macOS compatible with your Mac.

Shift-Option-⌘-R Install the macOS that came with your Mac, or the closest version still available.

Release the keys when you see the Apple logo, a spinning globe, or a prompt for a firmware password. When you see the Utilities window, you've started up from macOS Recovery.

Is it still able to boot from previous OS using alt key?

So how much free space did you have after downloading the mac OS installer program? And what version of the OS was installed and which version did you download?

Good luck

I have quit install, now I am back at the startup disk. Message is to select the system you want to use to start up your computer but nothing is listed. Any shortcut keys from here?