This process involves booting into single user mode.

1. Boot your computer while holding down Apple/Command + S on your keyboard.

2. At the command prompt type:

/sbin/fsck -y

3. Press Return on your keyboard.

4. Then at the command prompt type:

/sbin/mount -uaw

5. Press Return on your keyboard.

6. Next at the command prompt type:

rm /var/db/.applesetupdone

7. And finally at the command prompt type:

reboot

8. Then press Return on your keyboard and that is it - you are done! When your computer reboots you will have to go through the initial setup which is kind of a pain but it sure beats having to reinstall the operating system!