The metal part can be pulled out of the plastic key. Using a pair of needle nose pliers grasp the metal and pull the key off.
I had to change a key that had the wrong metal arm in it that I got from Paul, the top was the one I needed but the arm was wrong from my particular keyboard installation.  FYI, If you ever encounter a Keyboard that has Z and Y interchanged or an AZERTY keyboard you have to change the code bars in the keyboard if you want it to act like an American keyboard its not a simple fix like changing a top as the codes will still be wrong.

The key and metal are held in with friction. If the metal is rusty they can be "my ex wife" LOL! that said one came apart easy the other required some lube and muscle.
I can go take one apart and send a pic if you want.