If you look at the JJ Products web pages (jjproducts.net, I think) you will get some instructions on how to replace the standard arm rest (2nd Gen) with their wide arm rest. I have their replacement, and have taken the original one off. The notes above are correct. If you pry off the cap over the pivot point, you will be able to see the nut holding the arm rest in place. A socket set with an extender is helpful to easily turn the bolt.
(Surely your son received a big lump of coal in his stocking this year, and not that Miley Cyrus CD he wanted.)