The monkeys at Halfords won't have a clue unless it involves sticking their head in to see the back of the headlamp unit and unclipping the cover to access the bulb, which the D3 certainly doesn't.
You can either go in from the top and remove the airbox, or turn the wheels to full lock and undo a couple of screws in the wheelarch liner to peel it back and get your hand up to the back of the headlamp. But saying that, access might be slightly better in your V6 than it is with the V8s and V10
Either way, it's not the nicest of jobs and much swearing is usually involved. On that subject, I've got a little Ford Ka runaround and it's exactly the same on that - almost impossible to get to access from the engine bay unless you have fingers like toothpicks so you have to either remove the wheelarch liner or unbolt the whole front wing, simply to change a headlight bulb on a Ka.
I seem to remember OEM colour temperature is 4300K. I've gone for 5000k in the past when I replaced mine and been very happy with them. It's worth spending more ££ to get decent Philips or Osram bulbs, instead of generic Chinese eBay jobs. Not looked for a while but a pair is usually around £100 and sometimes down to around £80 on some websites.