Depends on which one, but this is not really a do-it-yourselfer job, and it's pretty messy. The first step is to get a copy of the manufacturer's service manual, then read through the pages of instructions with line drawings to see if you still want to tackle the job. You can also go to the top of this page, point to "Repair and Service", then click on "Manuals" to go to a web site where you can buy a subscription for your van. Normally I tell people to not bother with Chiltons and Haynes manuals because they only cover things do-it-yourselfers are expected to attempt, but in this case, I'll relent and let you use one if you can find one that isn't sealed so you can look inside to see if they cover this procedure.
If you're sure a line needs to be replaced, the most important thing to watch for is when you screw the soft metal nut into the rack and pinion steering gear assembly. Screw that in by hand at least three turns. Wash the threads off first with brake parts cleaner. If you "need" a wrench to turn the nut the first turn or two, it's cross-threaded. Forcing it won't be difficult with a wrench, but that will destroy the nut on the new line and the threads in the soft aluminum rack and pinion assembly. Warranty won't cover that.
If the old nut is corroded to the steel line, you can cut the line right above the nut, then use a ratchet with a six-point socket.