how do I erase an iMac
iMac with High Sierra mid 2011
iMac 21.5″
iMac with High Sierra mid 2011
iMac 21.5″
Also, if you intend to recycle, sell or give away the Mac please follow all the steps in What to do before you sell, give away, or trade in your Mac
Use Disk Utility to erase an Intel-based Mac - Apple Support
But that's only half the question. You also need to know how to install the OS unless you plan on recycling the device. Are you?
I have an old refurbished iMac with OS X El Capitan which I plan on recycling. How do I erase my content beforehand?
how do I erase an iMac