Lockset holes are the big holes in doors that accept door knob locksets. If you have an existing lockset hole and you are putting in a new lockset that requires a bigger hole, how in the world do you increase the size of the hole? The hole saws (which are really just big drill bits) used to drill these holes need material in the center of the hole for the pilot bit. Without material in the center of where the hole will be placed, hole saws can't be used.

The trick here is to get some scrap wood, plywood works great, and clamp it to the door over both sides of the existing hole. You can use C-clamps to hold the wood on. Once you have some plywood on both sides of the existing hole, you can use a hole saw to drill hole that will enlarge the diameter of the existing hole.