If it's there, proceed to the next step. But most Mac web browsers are setup with Stuffit Expander. Use Find File to look for it if you are uncertain on whether you have it installed on your Mac. If you don't have it, look on any Mac floppies or CD-ROMs you have for it, then install it. But you will need to transfer the file to your Mac in order to use it - a PC formatted floppy will do the trick.
Some people use both programs and create two ROM images.
Some say that each ROM image capture program handles ROMs differently. But you don't have to worry about that now. Double-click on the Stuffit Expander icon on the desktop. Now that Stuffit Expander is running, choose Unstuff from the File menu. This will open a dialog box like the one below.