How to Erase Files From My Mac Startup Diskby Alexander Poirier ; Updated September 28, 2017
A Mac computer's startup disk is the computer's default hard drive and the volume that the computer boots from. This drive can store all types of files, including applications, media, documents and more. If you need to delete files from your Mac computer's startup disk for any reason, you can do so in a few simple steps through the computer's Trash feature.
Click the "Finder" icon in the computer's dock.
Click the section of the computer's hard drive that contains the file you wish to delete beneath the "Places" heading. By default, there will be the "Desktop," "Applications," "User" and "Documents" options beneath the "Places" heading, but there may be other options depending on how you have customized your computer.
Click on the file you want to delete and drag the file onto the "Trash" icon in the computer's dock.
Hold the "Ctrl" key and click the "Trash" icon in the computer's dock.
Select the "Empty Trash" option from the context menu that appears. The file you placed in the Trash will now be erased from the computer's startup disk.