Hi, David.
Thank you for posting in the Apple Support Communities.
It sounds like you may have been experiencing a stall in downloading the macOS Big Sur upgrade. We’re not able to ascertain whether you were able to get upgraded in your other postings. Are you still experiencing the issue?
If you are, try these steps:
- Restart your Mac
- Restart your network equipment (e.g. Wi-Fi modem/router)
- Disconnect any external peripherals (e.g. external hard drives, audio devices, etc.)
- Delete the old installer before trying to download again. You can do this from the Applications folder in Finder (drag it to the trash) or from LaunchPad (click and hold the app until it shakes).
If you’re still not able to get the download to complete after these steps repairing your disk in First Aid from macOS recovery and trying to download from a new administrator account may also help.
Repair a storage device in Disk Utility on Mac - Apple Support
Set up users, guests, and groups on Mac - Apple Support
Respectfully.