how much bigger? A round or half moon wood rasp comes to mind, but I can't think of a power application to do the job.

You'd make a jig sized so that when the collar on a router followed it after having been clamped to the door, it would cut a perfect circle.

Skip to 5:30 please.

Context is key. Post more info and it may not be as simple as just a larger face bore. The backset size and depth comes into play and a larger hole while fitting the base of the lock may throw everything else way off.