empty imac

That all depends on what version of OS X came on it when it was new. If it is one of the newer download only versions, Lion or Mt Lion, then you use the Online Internet Recovery system, hold down the Command + Option/Alt + r keys until you see a globe on the screen, or if it came with DVD discs for reinstalling the OS and iLife programs.

Once that is known then the process is basically the same. Repartition the drive as One partition using Disk Utility, formatted Mac Extended (Journaled) with a partition table of GUID and then reinstall the OS. If it came with DVD discs then you supply those disc to the new owner.

To prepare a computer for sale or donation, in addition to the steps mentioned in this support article, take these steps:

• If you set a firmware password, remove it by running Firmware Password Utility in Recovery mode.
• If you activated FileVault in OS X 10.7 or later, turn it off.
• If you use Boot Camp, the partition must be deleted
• If you created any other data partitions on the internal drive, remove them in Disk Utility.
• Erase the data partition(s) with the option to zero out data. An SSD doesn't need to be zeroed.

The new owner will have to repurchase the software, if need be, under his or her Apple ID. If you ever updated the bundled iLife applications (Garage Band, iMovie, and iPhoto) through the App Store, you can't transfer them either.

Remove the machine from your list of registered products. If it's still covered by an AppleCare Protection Plan, transfer the coverage to the new owner by following the instructions in the AppleCare Terms and Conditions (under the heading "Transfer of Plan.")