Download Apple iMac Desktop Mockup Free PSD. Macintosh mockup to promote your designs. Now start publishing your designs on macintosh. However, to quickly give you an idea of how to edit the smart objects of the mockup, just double-click each smart object layer. A new document will open up where you can edit or add your pre-designed artwork and after you are done, just click save and your new work automatically updates in the mockup.