OS X Lion: Revert to a previous Mac OS X version
If you use Time Machine to back up your computer, you can easily revert to a previous version of Mac OS X if you experience trouble after installing an update.
- Choose Apple menu > Restart, and then hold down the Command (⌘) and R keys while the computer restarts.
- Select “Restore from a Time Machine Backup,” and then click Continue.
- Select your Time Machine backup disk.
- Select the Time Machine backup you want to restore. To restore your computer to the state it was in before you installed the new version of Mac OS X, choose the most recent backup.
- Follow the onscreen instructions.
If you backed up any individual files as described in the Important message above, you can restore them now. If you backed them up using Time Machine, recover them using the Time Machine application. (You can find the Time Machine application in the Dock or in the Applications folder.)