David wrote:

first of all you have to work upside down.
secondly, getting them perfectly parallel to the table requires at least
4 swear words.

I can't say that I share your experience.

I lock the head, pull the old blade, insert the new blade down into the
spring, and tighten the bolts. After rotating the head to the other
blade, repeat...

I've only done mine 4-5 times and never remember working upside down.
Maybe I'm doing it wrong, which wouldn't be a first!

Barry