How to start fresh on iMac?

[iNICK20]

I ordered and received a iMac on July 12/13 and was approved to return it for the new release one. I got it running Big Sur Beta. So how do I get running back to new state again? Do I need to remove Big Sur and go back to the previous OS? This is/was my first MAC ha.
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[Mr_Brightside_@]

Shut down, then boot up holding Command+R. This boots you to recovery mode. Erase your Macintosh HD using Disk Utility (make a backup first, of course).
Then, reinstall macOS. You're set.

 

[James_C]

I ordered and received a iMac on July 12/13 and was approved to return it for the new release one. I got it running Big Sur Beta. So how do I get running back to new state again? Do I need to remove Big Sur and go back to the previous OS? This is/was my first MAC ha.
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If you bought it from Apple then you can return it with Big Sur. Apple will wipe the hard disk. However make sure you sign out of iCloud and de-authorise any Apps that you need to (Office 365 for example). Of course if you are concerned about the security of your data you can wipe the machine yourself before sending it back to Apple. If you bought it from a 3rd Party supplier then for security I would definitely wipe and reinstall the OS.

Before you reinstall Catalina you should first remove the Mac from the Beta program as this will stop the beta updates from arriving on your Mac.

Here's what you should do:

Open System Preferences on your Mac.
Click on Software Update.
On the left side, under the cog icon, you will see the message: "This Mac is enrolled in the Apple Beta Software Program". If you want to stop receiving beta updates on you Mac click on Details.

A pop up will appear asking you to confirm that you want to restore default update settings. It will indicate that any current updates won't be removed but you will no longer receive beta updates. To confirm this click on Restore Defaults.

Then follow the advice given by @Mr_Brightside_@ above.

 

[Fishrrman]

The new iMac should come with a special version of the OS containing new, additional resources to help it boot the computer.

I would advise you to NOT try "experimenting with Big Sur" on the new one, at least for a while.
If something goes wrong, it may prove difficult to "get it back" to Catalina...