Insert an opening tool beneath one of the top corners of the key you wish to remove and angle it upwards until you feel it unclip.

Repeat at the other top corner.

You should now be able to lift the key cap off, moving it slightly in the direction of its lower edge.

On the underside of the key cap, notice the different sorts of clips at the top and bottom of the key. The top ones are designed to push on or pull off but the bottom ones push on only. For this reason, you must remove the key cap by first lifting the top corners (not the bottom) and re-engage the top clips first when you replace them.