Plenty of people have asked over time how to remove wiper arms. I did mine today and took photos. I think this will work on most postwar cars, as the Trico mounting design didn't change much over the years.
This shows how the arms attach to the splined hubs. The circle shows a little spring-steel clip that must be released in order to get the arms off the hubs.
Lisle sells a special tool for this (of course they do!) but it's hard to find, and you don't really need it. All you need is a right-angle awl or a hook-type tool that you can grab that clip with.
It helps if you have someone to help you with this, but you can do it yourself. Raise the arm and slide the hook behind the spring clip and pull away from the hub. Then use a small pry tool to lift the opposite edge of the arm, and it will slide right up and off.
BTW, this is what happens if you are too rough. See the broken bit of the drive hub? Someone else did this, not me. The hub is just pot metal, so if you hook that by accident - even using the special Lisle tool - you can break the casting. Luckily there's enough left on mine to engage the clips, but these are not serviceable apart from the pivot assembly, so if you break it, you need a whole new assembly. Be gentle!
Lots more pix (and words!) on my blog, but this is the condensed version. Hope it helps someone else!