My 2020 Mac can’t upgrade to new OS

Whatisit2020 wrote:

How to free up space to upgrade OS

Big Sur—Press release states that you will need 35.5 GB of free storage when upgrading from High Sierra or newer, and 44.5 GB when upgrading from an older versions.

Empty your Trash — Delete files and folders on Mac - Apple Support

https://support.apple.com/guide/mac-help/delete-files-and-folders-on-mac-mchlp1093/mac

How to free up storage space on your Mac - Apple Support

https://support.apple.com/en-us/HT206996

See used and available storage space on your Mac

https://support.apple.com/guide/system-information/see-available-storage-space-syspf9b375b9/10.14/mac/10.15

User tip: "Other and What Can I Do About It ?"

https://discussions.apple.com/docs/DOC-5142

If necessary Thin local snapshots :

ref: https://eclecticlight.co/2020/04/09/where-did-all-that-free-space-go-on-my-apfs-disk/

Try something like OmniDiskSweeper for a GUI to get a good look at itemized file size and location:

OmniDiskSweeper http://www.omnigroup.com/more