I have reset the imac to factory settings but now asking to install high sierra operating system, but can’t as says no space but can’t go in to clean up computer to install as have reset. Help?
You'll want to reboot the Mac in Recovery mode – press and hold Command-R (⌘R) at startup – launch Disk Utility and erase the internal HDD and then Reinstall macOS.
For guidance, please see: Use macOS Recovery on an Intel-based Mac - Apple Support
Also: How to reinstall macOS - Apple Support
You'll want to reboot the Mac in Recovery mode – press and hold Command-R (⌘R) at startup – launch Disk Utility and erase the internal HDD and then Reinstall macOS.
For guidance, please see: Use macOS Recovery on an Intel-based Mac - Apple Support
Also: How to reinstall macOS - Apple Support
Generally, people use "reset" to mean they've reinstalled the OS back to factory out of there box condition.
Here's how you install/reinstall an Apple OS: How to reinstall macOS - Apple Support
You may needto do this: Create a bootable installer for macOS – Apple Support (UK)
You'll need a working Mac to be able to make the bootable flash drive.
High sierra install after imac reset but no space but can’t get in to amend
