How do I erase my old iMac of all my content ready to return to Apple or for sale.
I have Time Machine back-up and Have set up my new iMac. All I need to do is make sure the old iMac is properly erased. I have gone through all the iCloud issues to opt out and make sure this old iMac is not 'mine any more. Apple give a good description of how to do this in prep my device.
BUT I can't find the best way to securely delete everything off my old iMac