How do you remove a melted garbage can from a concrete driveway?

Metal will scrape off. So will plastic, to some degree. It is difficult to find solvents for the plastics generally used in these containers. And, in addition, they are toxic as heck and will drive the material into the concrete. Dump some ice on the remains and let is cool for a while, then chip it off. If you want to go to the trouble, sandblast it a bit to finish the job. If the can caught fire and melted, you might have a bit of penetration into the concrete. Burning it off is a poor idea because it will damage the concrete, and it's probably against most ordinances to do something like that. Mechanical removal is best; avoid chemical actions like solvents or fire.