Problem: Your old Mac has maxed out its hard drive’s storage space, preventing you from saving anything new.
Fortunately, with macOS Sierra, your Mac can help free up space for you. It does this by creating purgeable storage, which J. D. Biersdorfer explained in her New York Times article as “automatically deleting files that you can always download again,” like purchased music or movie files. Here’s how you do it.
1. Update your Mac with macOS Sierra, which you can download here.
2. In the top left corner of your screen, click the Apple logo. Then click “About This Mac.” Once that window appears, click the “Storage” tab, and then “Manage.”
3. When the Manage window opens, click “Optimize.” Confirm, and you’re done. This will optimize your storage by deleting iTunes movies and TV shows you’ve already watched, email attachments stored in the cloud and other things that can be easily re-downloaded if needed. If you need them again, Apple has them saved on its servers.