I read through the link Cruzin gave below real quick, may so quick I missed it, but there was no mention of cracking the master cylinder resevoir. Could be he assumes we should all know that , and it was too simple to list, but... add to what he said cracking the cap at the begining. Then using a large clamp (I keep an 8" around just for this) bottom out the piston to make room for the new (and larger) pads. Make sure when you put things back together, you tighten cap, and then engage brakes with car off. Seating the pads for the first time with assist may cause them to drag.
Hope this helps.