It can be an easy job depending on how handy you are. I did mine without any difficulty at all. I helped another person (b E-Mail_m who totally muffed the job, broke off the brass adapter/reducer double-threaded thingy at the back side and bent the copper piping to the point that it had to be replaced.
If you are good with hand tools and have a modicum of common sense (lets say that you feel comfortable replacing a fuel pump or rebuilding a carburetor and are god a Tetris) then it probably can be done.
On the other hand, if the phrase "assembly required" has you phoning a friend then maybe not so much.
There are four O rings (including the two on the steam wand, and the valve seal (like a washer as found in some faucets). Be sure to also get some food-safe silicone lube to lube things up when assembling. The valve seat is stainless steel, so probably all you need are the parts mentioned above.