You'll need to remove the barrel using a receiver wrench and a barrel vice (don't clamp the receiver in a vice and try to unscrew the barrel with a pipe wrench, that's a no no). After replacing the barrel, you may also have to change the locking shoulder to adjust your headspace. At the minimum, you'll need a set of headspace gages to check headspace after replacing the barrel. At worst, you'll also need a new locking shoulder of the appropriate size and pin gages to figure out which locking shoulder is the appropriate size.
If you can find a smith in your area that can remove the existing device, you're probably better off that way. A wrench and barrel vice will probably set you back $100 at least. The pin gages will be another $40 or so for a full set. Then you have to buy a barrel. DSA sells brand new ones with the gas block installed for $175. If you then want to add evil features, such as a Stoll flash hider, you'll have to buy the evil feature and have it installed.
If you just want to change the barrel, check over at the FAL Files for a detailed walkthrough on installing and headspacing a barrel.