By default, the cartridge box is on the right most side of the printer. To get the printhead out, you need to disengage two tabs on the back of the cartridge box, shown on step 18. It's impossible to get to the right side one unless you can move the cartridge box close to the middle. And by default, you can't move the cartridge box by hand unless you unlock it on step 13, which is inside the side housing. If you can get away with sticking your hand inside the small rectangular hole of the top housing, then you don't have to take it off. But it's very difficult to maneuver your tweezers without lots of room. It's a tricky and awkward motion for your hand to disengage it, so we took off the housing first.
I'm not sure if any resets need to be done. You might have to realign the printhead using the printer software after you install it if the prints turn out strange.