Since I find myself performing that very task out in the parking lot of some auto parts store where the wiper inserts were purchased, I find that fingers do an okay job.

Each wiper blade has four contact points where it holds the insert. The insert is flexible enough to hold one end and bend slightly to coax out of one end, then do the same for the other. Then you'll have to squeeze the trailing end when it reaches each of the places where it meets the holder. It just takes patience...

Only reason I do this as opposed to replacing the whole unit, is because the OEM blades have the model of the car embossed on the blade! I'm a purist I guess...

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car