It is possible to on some models. Use two small knives from the cutlery drawer to lever it out, getting the knives either side, under the key.
Replacing it should be just a matter of popping the key back on and pushing down.
Do this when the computer is switched off for safety reasons, and there is no guarantee the key will go back on (if it isn't designed to be cleaned this way).
WD40 may not be the best idea, though as it may cause a short circuit or something. Again, it may not be best to do this.
As most people would, I advise to buy a new keyboard. They're cheap, better, and for health reasons, a keyboard should be replaced annually (in an ideal world - think of all the sneezing on the keyboard and dirt from the fingers building up).