I just did the wiper arm upgrade last week. It's so nice to have wipers that actually clean the windshield, and clean a large portion of the windshield to boot.
There is a small spring loaded clip on the wiper that holds it on. You have to hold the clip back while wiggling the blade off. Maybe try to spray a bit of penetrant up in if they've been on and idle for a long time.
Here's a couple photos