So the DIY covers the procedure - as for when to replace them, the maintenance minder usually tells you around the same time as the timing belt (105k miles or so) - the OEM plugs are iridium - NGK IZFR5K-11
You can use other plugs of the same geometry and heat range - they don't need to be iridium, but the iridium plugs last longer (and that's what the maintenance minder expects - so if you use copper plugs, you'll need to change them more quickly, and keep track of that on your own).
If you've never worked with iridium plugs before, be extremely careful checking the gap or trying to adjust them - the electrode is very easily damaged (snapped off)
Just replaced the plugs on my 05 yesterday, had my 13 year old helping. He did the three in front. Not that bad to do. The hardest is the one on the right on the rear, you just need to have some patience and care inserting the new plug into the tight space. Total time was less than 1 hour, that was including taking off the top plastic over the radiator and the front grill.
I had only 92k miles and from the looks of the plugs could have gone at least 10k more. There was only one plug that looked different, more color on the metal threads.
Make sure you use some anti seize on the threads when putting them in, and when you start screwing them in, go backwards until you feel it drop in, then start threading, this will prevent cross threading, especially for the rear plugs since you can not see a thing...
As stated, you need to use NGK IZFR5K-11. Cheapest is ordering from Advance Auto, you can find coupon codes. I had used 20 off 75 coupon. This is still good. Just use BIG20 for the code when you checkout. The plugs will be over 12.00 each, this will bring it down to 8.67 each. Add the anti seize to the order to get you over 75.