Currently Being ModeratedMay 6, 2012 8:12 PM (in response to scott244)
2 ways to go...
1. Insert the Mac OS X Install disc that came with your computer, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
*Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.*
3. Click the Erase tab.
4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
5. Select your Mac OS X volume.
6. Highlight the drive, select Partition Tab, then Format type... MacOS Extended Journalled, select the Security Options button, choose Zero Out Data, Erase... after completion do a new install.
Open System Preferences>Accounts, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.
In the same pref pane highlight your old account, click the little minus icon, then use Disk Utility to Secure Erase Free Space.
Currently Being ModeratedMay 6, 2012 8:21 PM (in response to scott244)
By the way if your machine did not ship with Lion then you cannot sell it with Lion for 2 reasons. First it's a violation of the licensing agreement and second the upgrade is tied to your AppleID. Follow BDAqua's instructions and you will be fine. Also don't forget to Deauthorize the computer in iTunes!
You also may find the Preparing your Mac for sale article useful.
Currently Being ModeratedMay 6, 2012 8:21 PM (in response to BDAqua)
Small amendments to BDAqua's post.
Step 1 has you insert the disc that came with the computer. This is okay if this is an iMac that came with Snow Leopard or earlier, but if it is a newer one that came with Lion there is no startup disc. Read these links for what to do in that case:
Lion - Disk Utility - https://discussions.apple.com/message/16925522 - repairing your drive using Disk Utility on Lion's recovery partition.
OS X Lion: About Lion Recovery Disk Assistant - http://support.apple.com/kb/HT4848 - Create recovery disk on another drive for when Lion's Recovery Partition does not work.
OSX: About Lion Recovery - http://support.apple.com/kb/HT4718 > Lion Internet Recovery - using the Internet to start when recovery disk partition not available.
Step 6 has you do a new Lion installation. This is again okay if the computer came with Lion, but if it came with an earlier system then the upgrade copy of Lion belongs to you, not the computer (a complete about face from when there were system discs and passing on the disc passed on ownership of the system). Make sure the new owner receives the discs that came with the computer (if any) and those for any system installed on the computer (if applicable).