Older steel frames can usually just be sprung out 5-6mm on a side, in my experience. Just spring the drops in or out, center the wheel with the chain appropriately tight, and tighten down the axle. Double check that the wheel is still centered. Eventually, the frame will take the new set. I've done this for years, on many many bikes with no failures whatsoever. If you have to change a LOT (Like say, 3-4cm total.) you probably need to have the frame set, or, if it's an aluminum or CF frame, then you need to get a bike shop to do it, or play with the spacers, washers, etc. Steel is forgiving that way.