8. Run First Aid on your disk

If any system files on your Macintosh HD are corrupted, the upgrade process

may fail. You can dramatically reduce the chance of this happening by checking for and repairing damaged files.

Close any applications that are currently open and then click on Spotlight at the top right of the screen. Type Disk Utility into Spotlight and press Enter. Click Macintosh HD on the left-hand side and then on the First Aid button at the top, then Run. Disk Utility will inform you if the repair has been successful.