He won't have to change the bolt head as both the cartridges have exactly same size rim diameter. He can get 1 of the spacers for magazine box (or box & follower) such as Savage has been doing for years. If you're dead set on another caliber/cartridge, trading would make the most sense cost wise. if determined to replace barrel on your existing action, it would make MUCH MORE sense to have a qualified gunsmith do it.
ORIGINAL: thndrchiken
You won't be able to rechamber the barrel you have. You can however pick up a 243 barrel from Midway that is fully chambered. You'll need the barrel, barrel nut wrench, barrel vise, head space gauges and an action wrench. You will also need to change the bolt head and most likely the magazine box and follower. By the time all is said and done it is cheaper to buy a gun chambered for the 243.