Apple iMac (21.5-inch, Late 2011) - Manual (Page 48)

48 Chapter 4 Problem, Meet Solution
You can install Mac OS X without erasing the disk, which saves your existing files
and settings, or you can erase the disk first, which erases all your data and leaves the
computer ready for you to reinstall Mac OS X and Apple applications.
After reinstalling Mac OS X, you can re-download the Apple applications that came
with your iMac and other apps you purchased from the Mac App Store. You can restore
your other data and applications from a Time Machine or other backup.
Important: Apple recommends that you back up the data on the disk before restoring
software. Apple is not responsible for any lost data.
Restoring Your Computer to Its Factory Settings
When you restore your computer to its factory settings, everything on your computer
(your user accounts, network settings, and all of your files and folders) is deleted. Before
you restore, back up any files you want to keep by copying them to another disk.
Write down your network settings from Network preferences to make it easier to get
connected again after reinstalling Mac OS X.
1 Make sure your iMac is connected to the Internet by using an Ethernet or Wi-Fi
network. (To connect to a Wi-Fi network, follow the instructions on page 46.)
2 In the Mac OS X Utilities pane, select Disk Utility and click Continue.
3 Select the disk in the list on the left, and then click the Erase tab.
4 Select Mac OS Extended (Journaled) from the Format pop-up menu, type a name for
the disk, and then click Erase.
5 After the disk is erased, choose Disk Utility > Quit Disk Utility.
6 In the Mac OS X Utilities pane, select Reinstall Mac OS X and click Continue.
7 To reinstall Mac OS X and your applications, follow the instructions in the Mac OS X
Installer.