View in HD at . When you Mac's hard drive is almost full, you can investigate and figure out what is using the space by simply using the Finder. There is no need to buy a third-party app to manage your hard drive. You start at the top and view all of your folders, digging down to see what is using the most space. Then you'll need to make some decisions about what to remove from yoru drive, being care to only remove files you don't need.