I am assuming your replacement inserts are the Bosch type.
There is a plastic tab on one end (or the other) that needs to come off first. Then, there is a V-shaped spring clip that you push inward to allow the blade to slide through the 4 pairs of hooks that hold the wiper assembly in place.
Or you could just buy a complete wiper assembly and be done with it!
I went with just replacing the blades...the OEM assemblies have "R129" embossed on the top...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car