how to factory reset macbook pro lion osx

Before you can erase you will need to unmount all partitions. To do this:

1. Select each partition on the left under your 500gb drive

2. Click the unmount icon/button

3. To prevent any issues, go to the partition tab on the right with the drive selected

4. Select each partition

5. Click the minus "-" button and confirm

6. Now you can select the whole drive and erase/format

Cheers

Hey I got the same problem, I can't erase my disk because it says, impossible to unmount, and when I try to delete the partition I says the same thing, even if it's unmounted.