Product review (5 stars): if the old cartridge doesn't come out fairly easily, then you need to push the old cartridge ...
This replacement water filter fits perfectly on our Kenmore Elite refrigerator.  Replacement was simple once I figured out the trick.  On my refrigerator (and apparently on most others that this filter works with), you open the little white filter compartment by pressing the small plastic tab, and the "door" opens.  Then you gently pull downward (not out) on the filter so it drops down at an angle.  At this point, you should be able to remove the old filter cartridge just by tugging gently.  Here's the key: if the old cartridge doesn't come out fairly easily, then you need to push the old cartridge a little farther downward so it's at more of an angle, and then try pulling it out again.  The new one just snaps into place.