1. Make sure your MacBook is turned off. 2. Press the Power button. 3. Immediately hold down the command and R keys. 4. Wait until the Apple logo appears. 5. Select “Disk Utility” from the OS X Utilities list. Click Continue. 6. Select the disk you’d like to erase by clicking on it in the sidebar. 7. Click the Erase button. 8. Click the Security Options button. 9. The Security Options window includes a slider that enables you to determine how thoroughly you want to erase your computer. Slide to "Fastest" 10. Once you’ve selected the level of secure erasing ("Fastest"), click the OK button. 11. Click the Erase button to begin.