Step 9: Remove the Plastic Retainer
Using a very small screwdriver or blade type tool, very carefully pry all around the edge of the plastic retainer. It will only come up a teeny bit before it lets go.
Set the retainer to the side.
You can now try simply dumping the last part out of this section of the cartridge since the retainer is no longer there to keep it. However, if it does not freely fall out, this may be the problem with the cartridge.
Using a flat blade screwdriver, insert the screwdriver into the end where the retainer was and gently twist the inside section to break it loose. Next, using the holes along this unit, help the inside piece to come completely out.