it was called the Amiga, and the upgrade was to buy a whole new box and whole new software. But it didn't work out, despite being better than what Jobs or Billy and Bally and a PC Cloners had to offer against it. There was emulation software to run PET, C64, VIC-20, etc software on the Amiga, not to mention PC (8088), Macintosh, Apple //, and others. I had an Amiga 1020 5.25" floppy drive that could read 360K PC/MS-DOS floppies, 1571/1541/PET C= floppies, and more.
But Comodore could not shake that "Toy Computer" MOTIF that most people gave it.